Blood substitute composition and method of use

ABSTRACT

The present disclosure provides oxygen-carrying nanoparticles, methods of making the nanoparticles, and methods of using the nanoparticles to carry oxygen in blood.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of U.S. Ser. No. 15/232,298, filed,Aug. 9, 2016, which is a continuation of U.S. Ser. No. 14/930,396, filedNov. 2, 2015, which claims the priority of PCT ApplicationPCT/US2014/036762, filed May 5, 2014, which claims the benefit of U.S.provisional application No. 61/819,426, filed May 3, 2013, each of whichis hereby incorporated by reference in its entirety.

GOVERNMENTAL RIGHTS

This invention was made with government support under HL094470 andNS073457 awarded by National Institutes of Health. The government hascertain rights in the invention.

FIELD OF THE INVENTION

The present disclosure generally relates to nanoparticles comprising anoxygen-carrying composition, methods of making the nanoparticles, andmethods of using the nanoparticles to carry oxygen in blood.

BACKGROUND OF THE INVENTION

Blood transfusions are life-saving procedures used in medical conditionsand emergencies to replace lost components of the blood. According tothe American Red Cross, someone in the U.S. needs blood every twoseconds, more than 44,000 blood donations are needed every day, and atotal of 30 million blood components are transfused each year in theU.S. A single car accident victim can require as many as 100 pints ofblood. In addition, patients with diseases such as sickle cell anemiaand cancer affect millions of people in the U.S., and patients withthese diseases can require frequent blood transfusions throughout theirlives. Major worldwide blood shortages, infected donated blood, thenecessity for blood typing, a short shelf life of stored blood, and theinadequacy of stored blood for use in certain situations such asbattlefield scenarios and trauma, have led scientists to synthesize andtest blood substitute products. Although non-blood volume expanders forcases where only volume restoration is required are widely available, todate there is no well accepted oxygen-carrying blood substitutes.Perfluorocarbon based oxygen-carrying products rely ondissolved oxygen,dissolve 3 times more in oxygen than red blood cells, and have a longshelf life. However, PFC-based products have failed due to poor oxygendelivery functionality, short half-life in circulation, complementactivation by pluronic surfactants in PFC-based products, and requirecold storage at freezing temperatures. On the other hand, currentlyavailable hemoglobin based oxygen carriers (HBOCs) have a short periodof functionality during circulation, have poor oxygen capture andrelease dynamics, and are incompatible with dry storage, limiting theiruse in remote areas. In addition, hemoglobin based oxygen carriers havebeen shown to be unsafe, causing hemodynamic and gastrointestinalperturbations related to nitric oxide (NO) scavenging, free radicalinduction, and alteration of biochemical and hematological parameterssuch as increased liver enzyme levels and platelet aggregation.

Therefore, there is a need for a safe and efficient oxygen-carryingblood substitute having adequate oxygen capture and release dynamicsthat does not interfere with normal regulation of blood vessel caliber,is capable of maintaining oxygen-carrying functionality duringcirculation, and is amenable to extended storage and ease of use.

SUMMARY OF THE INVENTION

Accordingly, in one aspect, the present disclosure provides anoxygen-carrying nanoparticle. The nanoparticle has a substantiallybi-concaved disc shape, comprises an aqueous core and a shell comprisingan amphiphilic polymer. The nanoparticle also comprises anoxygen-carrying agent, an allosteric effector, and a reducing agent. Theamphiphilic polymer may comprise a branched polymer conjugated to alipid. The surface of the amphiphilic polymer comprising the outer layerof the shell may be derivatized with polyethylene glycol. The averagediameter of the nanoparticle may be from about 150 nm to about 300 nm,and the average height of the nanoparticle is from about 30 nm to about80 nm. The nanoparticle may comprise a through-hole or a depression. Theamphiphilic polymer may comprise polyethyleneimine conjugated toC24-pentacosadiynoic acid. The amphiphilic polymer may also comprisepolyethyleneimine conjugated to palmitic acid. The oxygen-carrying agentmay be hemoglobin. The allosteric effector may be 2,3-DPG. The reducingagent may be leucomethylene blue. The nanoparticle may comprise about20% to about 60% (w/v) hemoglobin. The nanoparticle may belyophilizeable and stored for extended periods at ambient conditions.The lyophilized nanoparticles may be reconstituted in an aqueous bufferat various concentrations prior to administration. The nanoparticle maynot substantially sequester nitric oxide. The nanoparticle may limit theoxidation of hemoglobin to about 10% or less of the total concentrationof hemoglobin in the nanoparticle.

In another aspect, the present disclosure provides a process for thepreparation of an oxygen-carrying nanoparticle. The nanoparticle has asubstantially bi-concaved disc shape, comprises an aqueous core and ashell comprising an amphiphilic polymer. The nanoparticle also comprisesan oxygen-carrying agent, an allosteric effector, and a reducing agent.The process comprises hydrophobically modifying a branched polymer bycovalently linking lipids to free reactive groups of the polymer to forman amphiphilic polymer. The amphiphilic polymer is then mixed with anon-polar solvent. The mixture is agitated to form a plurality ofinverted micelles comprising the amphiphilic polymer. The invertedmicelles are then agitated in the presence of heat and an aqueoussolvent to form the bi-concaved disc shaped nanoparticles. Theoxygen-carrying agent, the allosteric effector, and the reducing agentare added to the nanoparticles and the mixture is agitated to load theoxygen-carrying agent, the allosteric effector, and the reducing agentinto the nanoparticles. The oxygen-carrying agent, the allostericeffector, and the reducing agent may be contained within the aqueousinner core of the nanoparticle.

In another aspect, the present disclosure provides a process for thepreparation of an oxygen-carrying nanoparticle. The nanoparticle has asubstantially bi-concaved disc shape, comprises an aqueous core and ashell comprising an amphiphilic polymer. The nanoparticle also comprisesan oxygen-carrying agent, an allosteric effector, and a reducing agent.The process comprises hydrophobically modifying a branched polymer bycovalently linking lipids to free reactive groups of the polymer to forman amphiphilic polymer. The amphiphilic polymer is then mixed with anon-polar solvent. The mixture is agitated to form a plurality ofinverted micelles comprising the amphiphilic polymer. The invertedmicelles are then agitated in the presence of heat and an aqueoussolvent to form the bi-concaved disc shaped nanoparticles. Theoxygen-carrying agent, the allosteric effector, and the reducing agentare added to the nanoparticles and the mixture is agitated to load theoxygen-carrying agent, the allosteric effector, and the reducing agentinto the nanoparticles. The oxygen-carrying agent, the allostericeffector, and the reducing agent may be contained within the aqueousinner core of the nanoparticle.

In yet another aspect, the present disclosure provides a bloodsubstitute composition. The composition comprises an oxygen-carryingnanoparticle. The nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a shell comprising an amphiphilicpolymer. The nanoparticle also comprises an oxygen-carrying agent, anallosteric effector, and a reducing agent. The blood substitutecomposition may comprise from about 4×10¹² to about 4×10¹³nanoparticles/ml. The blood substitute may be reconstituted in a fashionthat is tailored to the status of a patient's circulating blood volume;the blood substitute may be composed in a more concentrated fashion tobe administered to normovolemic subjects (e.g. a subject with anemia) orin a more dilute fashion to be administered to hypovolemic patients(e.g. a subject with hemorrhage).

In another aspect, the present disclosure provides a method ofsupplementing the oxygen-carrying capacity of a subject's blood. Themethod comprises, administering to the subject an effective amount of anoxygen-carrying nanoparticle. The nanoparticle has a substantiallybi-concaved disc shape, comprises an aqueous core and a shell comprisingan amphiphilic polymer. The nanoparticle also comprises anoxygen-carrying agent, an allosteric effector, and a reducing agent.When administered to subjects with symptomatic anemia or hemorrhage, theadministered nanoparticle will capture O₂ during perfusion through thelungs and subsequently, deliver O₂ to tissue during systemic perfusion.O₂ delivery to tissue by the nanoparticle will be enabled by thefollowing key nanoparticle design features: (1) The nanoparticle shellprevents trapping of nitric oxide by an oxygen carrying agent (e.g.hemoglobin, modified hemoglobin, leghemoglobin, hemin, or others)permitting endogenous signaling that normally routes blood flow to areasof O₂ delivery lack. (2) The nanoparticle payload contains anheterotropic allosteric effector molecule (e.g. 2,3-DPG or others),which modifies the oxygen carrying agent's O₂ affinity; the freeconcentration of the allosteric effector in the particle core ismodulated by pH-responsive binding to the nanoparticle inner shell—sothat the allosteric effector is sequestered to the inner shell duringlung perfusion (at high pH, thereby increasing the oxygen carryingagent's O₂ affinity and facilitating O₂ capture) and the allostericeffector oxygen carrying agent's is released from the inner shell duringsystemic perfusion (low pH, thereby lowering the oxygen carrying agent'sO₂ affinity and facilitating O₂ release). This effect is amplified insettings of physiologic need [with lung pathology, hyperventilationraises pH and enhances O₂ capture; with tissue hypoxia, anaerobicmetabolism lowers pH and enhances O₂ release]. (3) The nanoparticlepayload contains a reducing agent (e.g. leucomethylene blue,glutathioine, ascorbate or others) which recycles oxidized oxygencarrying agent, extending effective circulating time for thenanoparticle. Thereby the nanoparticle will effectively release O₂during perfusion across the O₂ tensions/gradients encountered innormal/abnormal physiology (e.g. in a human, tissue pO₂ ranges from 40to 5 Torr).

In an additional aspect, the present disclosure provides a method forconducting the administration of an oxygen carrying nanoparticle into asubject. The method comprises transfusing a solution comprising anoxygen-carrying nanoparticle into the subject. The nanoparticle has asubstantially bi-concaved disc shape, comprises an aqueous core and ashell comprising an amphiphilic polymer. The nanoparticle also comprisesan oxygen-carrying agent, an allosteric effector, and a reducing agent.

In another aspect, the present disclosure provides a method ofsupplementing the oxygen-carrying capacity of a subject's blood. Themethod comprises, administering to the subject an effective amount of anoxygen-carrying nanoparticle. The nanoparticle has a substantiallybi-concaved disc shape, comprises an aqueous inner core and ahydrophilic outer shell comprising an amphiphilic polymer. Thenanoparticle also comprises hemoglobin or synthetic hemoglobin, 2,3-DPG,and leucomethylene blue. When administered to subjects with symptomaticanemia or hemorrhage, the administered nanoparticle will capture O₂during perfusion through the lungs and subsequently, deliver O₂ totissue during systemic perfusion. O₂ delivery to tissue by thenanoparticle will be enabled by the following key nanoparticle designfeatures: (1) The nanoparticle shell prevents trapping of nitric oxideby hemoglobin or synthetic hemoglobin, permitting endogenous signalingthat normally routes blood flow to areas of O₂ delivery lack. (2) Thenanoparticle payload contains 2,3-DPG, which modifies Hb O₂ affinity;the free concentration of 2,3-DPG in the particle core is modulated bypH-responsive binding to the nanoparticle inner shell—so that 2,3,-DPGis sequestered to the inner shell during lung perfusion (at high pH,thereby increasing HbO₂ affinity and facilitating O₂ capture) and2,3-DPG is released from the inner shell during systemic perfusion (lowpH, thereby lowering HbO₂ affinity and facilitating O₂ release). Thiseffect is amplified in settings of physiologic need [with lungpathology, hyperventilation raises pH and enhances O₂ capture; withtissue hypoxia, anaerobic metabolism lowers pH and enhances O₂ release].(3) The nanoparticle payload contains leucomethylene blue which recyclesoxidized Hb, extending effective circulating time for the nanoparticle.Thereby the nanoparticle will effectively release O₂ during perfusionacross the O₂ tensions/gradients encountered in normal/abnormalphysiology (e.g. in a human, tissue pO₂ ranges from 40 to 5 Torr).

DESCRIPTION OF THE FIGURES

The application file contains at least one photograph executed in color.Copies of this patent application publication with color photographswill be provided by the Office upon request and payment of the necessaryfee.

FIG. 1A-F depicts the preparation and various characteristics ofnanoparticles comprising hemoglobin. (A) Schematic representation ofnanoparticle preparation and schematic representation of nanoparticles.(B) A plot showing the variation of nanoparticle sizes in a preparationof nanoparticles. (C) A plot showing the variation of particle size oflyophilized and non-lyophilized nanoparticles with time. (D)Transmission electron microscope image of nanoparticles drop-depositedover nickel grid. (E) Magnified view of squared-off portion oftransmission electron microscope image of nanoparticles in D. (F) Atomicforce microscope image of nanoparticles.

FIG. 2A-D depicts oxygen binding-dissociation curves of nanoparticlesmeasured at pH 10 (dark blue curves), 9 (green curves), 8.5 (magentacurves), 8 (light blue curves), and 6 (red curves). (A) Oxygenbinding-dissociation curves of oxygen-carrying nanoparticles labeledwith leucobenzyl methylene blue. (B) Oxygen binding-dissociation curvesof the oxygen-carrying nanoparticles in (A) after about five days instorage. (C) Oxygen binding-dissociation curves of unlabeledoxygen-carrying nanoparticles. (D) Oxygen binding-dissociation curves ofthe unlabeled oxygen-carrying nanoparticles in (C) after about five daysin storage.

FIG. 3A-B depicts graphs showing the rheological properties (A) andpharmacokinetic profile (B) of a nanoparticle. (A) Nanoparticle:plasmasuspensions of 1:9 and 1:10 in volumetric ratio to NZW (rabbit) plasmawere studied at 37.1° C. using data points corresponding to at least 10%torque (Wells-Brookfield Cone/Plate Viscometer). The viscosity againstshear rate plots revealed the nanoparticles had no effect on the plasmaviscosity. (B) Nanoparticle hemoglobin was radiolabeled with a ^(99m)Tctracer dose (50 μCi/kg) and administered to rats (n=3). Blood sampleswere drawn at 0, 5, 20, 40, 60, 90, 120, 150, minutes postadministration into heparinized micro capillary tubes, sealed, and 10 μlaliquots drawn into a micro syringe was placed in plastic tubes, capped,and counted using an automated well gamma counter (Perkin-Elmer, Wizard3). Findings illustrate bi-exponential clearance typical fornanoparticles of this particular size range.

FIG. 4 graphically depicts representative traces from an NOsequestration assay of the four different nanoparticle formulationsdescribed in Table 2. Inset, sample F-3 has been excluded, to give aclearer picture of other responses. Sample injections are equimolar forheme, data are normalized to permit overlapping.

FIG. 5 graphically depicts representative traces from an NOsequestration assay of RBCs, cell-free Hb and two different nanoparticleformulations, F-3 and F-4 (see Table 2). Samples are equimolar for heme.Data are normalized to permit overlapping. Inset: Initial sequestrationrate for each sample (trend lines fitted to the first 10 seconds ofdata).

FIG. 6 is a bar graph depicting the total NO scavenged for fournanoparticle formulations (F-1, F-2, F-3, and F-4; see Table 2) incomparison to physiological controls (RBCs and cell-free Hb). Total areaunder curve (AUC) represents total NO sequestered. All samples areequimolar for heme. *p<0.05; one way ANOVA (n=5). All nanoparticleformulations differ from RBC and Hb samples.

FIG. 7 is a bar graph depicting NO sequestration rate for fournanoparticle formulations (F-1, F-2, F-3, and F-4; see Table 2) incomparison to physiological controls (RBCs and cell-free Hb). Theinitial rate of NO scavenging was calculated by fitting a tread line tothe first ˜1 min of data following sample injection. *p<0.05; one wayANOVA (n=5). Cell-free Hb sequesters NO more avidly than do intact RBCs(as is known); all nanoparticle formulations sequester NO less avidlythan RBCs, with the exception of F-3 (equivalent to RBCs).

FIG. 8A-L depicts graphs and images showing whole body and tissue HIFlevels vary as a function of [Hb] in HIF-α(ODD)-luciferase mice. (A-B)Whole body HIF-luciferase level was significantly increased duringhemodilutional anemia. In (A) depicts HIF-luciferase levels graphically,and (B) depicts images of the whole animal. (C-E) Tissue-specificHIF-luciferase luminescence changes in a similar fashion; brain (C),kidney (D) and liver (E). (F-G) Similar to (C-E), measurement of brainHIF-1 α protein expression by western blot increased proportionally withhemodilution. (F) depicts an image of a western blot of HIF-α and acontrol (α-tubulin); in (G), the levels of HIF-α protein are graphicallydepicted. (H-J) Likewise, selected HIF-dependent mRNA levels increase aswell: (H) GLUT1, (I) PDK1, (J) MCT4. (K-L) Depicts images and graphsshowing the relationship of Hb levels and whole body HIF luciferase.Specifically, HIF luciferase signal is inversely related to Hb duringboth development of, and resolution from, anemia. (K) whole body imagingand (L) normalized body radiance (left y-axis) or hemoglobinconcentration (right y-axis) vs. anemia (x-axis). NB: Pairedmeasurements of brain pO₂ during acute hemodilution (by phosphorescencequenching) correlate with [Hb], affirming analysis HIF expressiontrends. For the following measurements of ([Hb](g/L) & pO₂ (mmHg),(mean±SD)), N=8 mice: Hb of 125.1±8.3→pO₂ of 65.0±8.3; Hb of88.3±5.4→pO₂ of 56.4±9.5; Hb of 72.5±7.4→pO₂ of 52.1±10.3; Hb of52.4±3.9→pO₂ of 40.6±6.8.

FIG. 9A-C depicts graphs showing the efficacy of a nanoparticle in arodent hemorrhagic shock model. The graphs in (A) and (B) illustrates anexpected, striking increase in the AV O₂ difference with blood removal(rising from 24 to 67%), that (A) persisted following resuscitation withnormal saline and (B) resolved following resuscitation with the bloodsubstitute (normalizing from 67 to 31%). (C) A difference was notobserved in the hemodynamic effect afforded by either resuscitationfluid (Normal Saline=NS, Nanoparticle Solution=NP), suggesting that thebenefit in O₂ delivery from the blood substitute arises from improved O₂content, in addition to restoration of blood pressure.

DETAILED DESCRIPTION

The present disclosure provides oxygen-carrying nanoparticles that aremorphologically similar to red blood cells. Oxygen-carryingnanoparticles of the disclosure are self-assembled, which means they arerelatively quick and easy to prepare. Oxygen-carrying nanoparticles ofthe disclosure are also substantially bi-concaved disc shaped providingincreased mechanical stability. Oxygen-carrying nanoparticles of thedisclosure comprise a payload. The payload comprises an oxygen-carryingagent, an allosteric effector and a reducing agent. Advantageously, anoxygen-carrying nanoparticle of the disclosure is capable ofincorporating high per particle payload, and is capable of mimicking theoxygen-carrying characteristics of red blood cells by shifting theaffinity of the oxygen-carrying agent to oxygen based on tissue need. Inaddition, an oxygen-carrying nanoparticle does not alter vascular tone,is capable of maintaining oxygen-carrying functionality duringcirculation, and avoids tissue extravasation throughreticuloendothelial-based particle clearance. Importantly, nanoparticlesof the disclosure may be lyophilized for extended storage, and may berapidly reconstituted before use.

Solutions comprising nanoparticles and methods of using thenanoparticles and solutions are also described.

I. Nanoparticle

One aspect of the disclosure provides a substantially bi-concaved discshaped oxygen-carrying nanoparticle. The nanoparticle comprises anaqueous core, a shell comprising an amphiphilic polymer, and a payload.The payload comprises an oxygen-carrying agent, an allosteric effector,and a reducing agent. Each aspect of a nanoparticle is described indetail below. Nanoparticles may also be as described in U.S. PatentApplication No. 2010/0297007, the disclosure of which is incorporatedherein by reference in its entirety.

(a) Morphology

A nanoparticle comprises a toroidal, i.e., substantially bi-concaveddisc shape. Such nanoparticles have a generally rounded, plate-like formof finite thickness which is concave on both surfaces, mimicking theshape of a human red blood cell, and increasing the surface area of ananoparticle when compared to a spherical nanoparticle, thereforeenhancing oxygen exchange dynamics of an oxygen-carrying nanoparticle.The concavity of the nanoparticles may take the form of a concavedepression on each surface, or an opening, or “through-hole” through theapproximate center of the disc. Within a population of nanoparticles,some of the nanoparticles may comprise a depression, and some of thenanoparticles may comprise a through-hole. In general, at least about50% of a population of nanoparticles may be bi-concaved disc shaped. Thepercentage of bi-concaved disc shaped nanoparticles may be about 50%,51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%,65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%,79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%,93%, 94%, 95%, 96%, 97%, 98%, or 99% of the total population ofnanoparticles. Alternatively, the percentage of bi-concaved disc shapednanoparticles may be at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%,85%, 90%, 95%, 97%, 98%, or 99% of the total population ofnanoparticles.

Because of the shape of nanoparticles, the diameter of a nanoparticle isgreater than the height of the nanoparticle. In general, the diameter ofa nanoparticle may range from about 50 nanometers to about 500nanometers, and the height of a nanoparticle may range from about 20nanometers to about 150 nanometers. As such, the diameter of ananoparticle may range from about 100 nanometers to about 300nanometers, and the height of a nanoparticle may range from about 40nanometers to about 85 nanometers. Alternatively, the diameter of ananoparticle may range from about 100 nanometers to about 250nanometers, and the height of a nanoparticle may range from about 30nanometers to about 80 nanometers. Preferably, the diameter of ananoparticle may range from about 120 nanometers to about 250nanometers, and the height of a nanoparticle may range from about 50nanometers to about 70 nanometers. The diameter of a nanoparticle mayalso be about 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200,210, 220, 230, 240, 250, 260, 270, 280, 290, or 300 nanometers, and theheight of a nanoparticle may be about 40, 45, 50, 55, 60, 65, 70, 75,80, or 85 nanometers.

Nanoparticles comprising a population of nanoparticles are substantiallyuniform in size, wherein size is measured as the diameter of ananoparticle. The variation in size among nanoparticles of thepopulation is less than about 15%. Preferably, the variation in sizeamong nanoparticles of the population may be less than about 10%, andeven more preferably less than about 5%. The variation in size amongnanoparticles of the population may be less than about 10%, 9%, 8%, 7%,6%, 5%, 4%, 3%, 2%, or 1%.

The size between two or more populations of nanoparticles can and willvary, wherein size is measured as the diameter of a nanoparticle. Sizeof a nanoparticle may be influenced by the types and concentrations ofoxygen-carrying agent, allosteric effector, reducing agent, andamphiphilic polymer and/or optional agents. While not wishing to bebound by theory, it is believed the size of a nanoparticle may increasewith increasing concentrations of oxygen-carrying agent, allostericeffector, reducing agent and/or optional agents. The size of ananoparticle may also increase with as the molecular weight of thebranched polymer comprising the amphiphilic polymer increases.

In general, bi-concaved disc shaped nanoparticles have increasedstability relative to non-bi-concaved disc shaped nanoparticles.Stability may be measured by changes in the particle diameter, zetapotential and/or polydispersity over time. Stability may also bemeasured by changes in the release of the payload over time (e.g.release of an oxygen-carrying agent, allosteric effector and/or reducingagent over time). A stable nanoparticle may reflect less than about 20%,preferably less than about 15%, more preferably less than about 10%change from baseline properties. Bi-concaved disc shaped nanoparticlesare stable at room temperature for at least several months, for morethan two months, or for more than three months. Stability is typicallymeasured for a population of nanoparticles rather than a singlenanoparticle. In general, bi-concaved disc shaped nanoparticles arestable at 4° C. for at least several months, or for more than twomonths. Further details are provided in the Examples.

(b) Shell

A shell of a bi-concaved disc shaped nanoparticle comprises anamphiphilic polymer, wherein the amphiphilic polymer comprises abranched polymer covalently conjugated to lipids. The shell may alsocomprise water, a buffer solution, a saline solution, a serum solution,and combinations thereof. The shell may further comprise a biologicallyactive agent, an imaging agent, a metal atom, or a therapeutic agent, asdetailed below.

A shell of a bi-concaved disc shaped nanoparticle is bi-layered,comprised of a hydrophilic outer layer, a hydrophilic inner layer, and ahydrophobic region between the layers. To form the shell of ananoparticle, an amphiphilic polymer first self-assembles to form abi-layer comprised of a hydrophilic outer layer, a hydrophilic innerlayer, and a hydrophobic region between the layers, and thenself-assembles into a bi-concaved disc shaped nanoparticle. Theformation of the bi-concaved disc shaped particle is driven by thehydrophobic-hydrophilic block ratio of the amphiphilic polymer and theself-assembly procedure of the nanoparticles.

The amphiphilic polymer may comprise from about 1% to about 40% byweight of the nanoparticle. For example, the amphiphilic polymer maycomprise about 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%,6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%,13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%,19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%,25%, 25.5%, 26%, 26.5%, 27%, 27.5%, 28%, 28.5%, 29%, 29.5%, 30%, 30.5%,31%, 31.5%, 32%, 32.5%, 33%, 33.5%, 34%, 34.5%, 35%, 35.5%, 36%, 36.5%,37%, 37.5%, 38%, 38.5%, 39%, 39.5%, or about 40% by weight of thenanoparticle. The amphiphilic polymer may comprise from about 1% toabout 15%, about 5% to about 20%, about 1% to about 10%, or about 10% toabout 20% by weight of the nanoparticle. Alternatively, the amphiphilicpolymer may comprise from about 1% to about 5%, about 5% to about 10%,about 10% to about 15%, or about 15% to about 20% by weight of thenanoparticle.

Additional aspects are described in detail below.

i. Branched Polymers

A branched polymer may be a branched, amine-containing polymer with oneor more free reactive group. Non-limiting types of suitable branchedpolymers include star branched polymers, graft branched polymers, combbranched polymers, brush branched polymers, network branched polymers,hyperbranched polymers, and dendritic polymers.

The polymer may be a synthetic polymer, a semi-synthetic polymer, or anatural polymer. Non-limiting examples of suitable polymers includepolyacrylate, polyacrylamide, polyacrylamide sulphonic acid,polyacrylonitrile, polyamines, polyamides, polyamidoamine (PAMAM),polybutadiene, polydimethylsiloxane, polyester, polyether, polyethylene,polyethylene glycol (PEG), polyethyleneimine (PEI), polyethyleneoxide,polyethyleneglycol, polyethyloxazoline, polyhydroxyethylacrylate,polyisoprene, polymethacrylate, polymethacrylamide,polymethylmethacrylate, polymethyloxazoline, polyoxyalkylene oxide,polyphenylene, polypropyleneimine, polypropylene oxide, polystyrene,polyurethane, polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose,carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,hydroxy-propylmethylcellulose, hyaluronic acid, dextran, dextrin,heparan sulfate, chondroitin sulfate, heparin, alginate, agar,carrageenan, xanthan, guar, polyamino acids (such as e.g., polylysine,polyglycine, and polyserine), co-polymers, and combinations thereof.

A branched polymer comprises at least one type of reactive group.Suitable reactive groups include, but are not limited to, primary,secondary or tertiary amines, carboxylate, hydroxyl, alkyl, fluoroalkyl,aryl, acetate, amide, ester, sulfone, sulfoxide, sulfonate, sulfonamide,phosphonate, and phosphonamide groups.

The average molecular weight of a branched polymer can and will vary.For example, polymers of an increasing molecular weight may be selectedto produce an outer shell of an increasing thickness. The molecularweight may be expressed as the number average molecule weight (M_(n)) orthe weight average molecule weight (M_(w)). In general, the number andweight average molecular weight of a branched polymer may range fromabout 200 to about 1,000,000 Daltons. The number and weight averagemolecular weight of a branched polymer may range from about 200 to about50,000 Daltons, including from about 200 to about 5,000, from about5,000 to about 50,000, from about 50,000 to about 250,000, or from about250,000 to about 1,000,000 Daltons. Preferably, the number and weightaverage molecular weight of a branched polymer may be about 10,000Daltons, about 25,000 Daltons, or about 50,000 Daltons.

While not wishing to be bound by theory, it is believed the inherentnature of a branched polymer enables retention of an allosteric effector(described in Section I(f)) via electrostatic interaction. One skilledin the art will appreciate that the choice of branched polymer mayinfluence this interaction. For example, when a branched polymer is acationic branched polymer with secondary or tertiary amines, the aminedensity may be an important factor. It is not necessary, however, for abranched cationic polymer to be a cationic branched polymer toelectrostatically interact with an allosteric effector. For making anelectrostatic interaction with an allosteric effector, the amines of abranched polymer are sufficient. Preferred branched polymers mayinclude, but are not limited to, a polyethyleneimine branched polymer, aPAMAM dendrimer, a star polymer, or a graft polymer. Even morepreferably, the branched polymer is a polyethyleneimine branchedpolymer. An exemplary branched polymer is a 10K polyethyleneiminebranched polymer, a 50K polyethyleneimine branched polymer, or a 100Kpolyethyleneimine branched polymer. An exemplary branched polymer is G4polyamidoamine.

ii. Lipids

An amphiphilic polymer also comprises lipids linked to a branchedpolymer. A lipid may be covalently linked or non-covalently linked to abranched polymer. While not wishing to be bound by theory, it isbelieved the percentage of reactive groups of a branched polymer linkedto lipids influences the hydrophobic character, and thus morphology, ofthe particle. The percentage of free reactive groups of a branchedpolymer linked to a lipid will vary with the materials in order tocontrol the hydrophobic-hydrophilic block ratio, which drives theformation of bilayer-type membranes into biconcave disc-like shapedparticles. Generally, an amphiphilic polymer comprises lipids linked toa branched polymer, wherein at least about 25% of reactive groups of abranched polymer are linked to lipids. For example, the percentage offree reactive groups linked to lipids may be 25%, 26%, 27%, 28%, 29%,30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%,44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%,58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%,72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%,86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or100%. The percentage of reactive groups linked to lipids may also be atleast about 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or 75%, orgreater than 75%. Preferably, the percentage of free reactive groupslinked to lipids may range from about 40% to about 70% or from about 50%to about 60%. An exemplary percentage of free reactive groups linked tolipids may be about 55%.

Non-limiting examples of suitable lipids include fatty acids, fatty acidesters, phospholipids, bile acids, glycolipids, aliphatic hydrophobiccompounds, and aromatic hydrophobic compounds. A lipid may be natural,synthetic, or semi-synthetic. In general, a lipid comprises a polar headgroup and at least one hydrophobic hydrocarbyl or substitutedhydrocarbyl group. A polar head group links a lipid to a branchedpolymer via a covalent bond. Examples of suitable polar head groupsinclude, but are not limited to, carboxy, acyl, propargyl, azide,aldehyde, thiol, ester, sulfate, and phosphate. Preferred hydrophobichydrocarbyl groups include, but are not limited to, alkyl, alkynyl,heterocylic, and combinations thereof. Typically, alkyl or alkynylgroups comprise from about six to about 30 carbon atoms, or morepreferably from about 12 to about 24 carbon atoms. A substitutedhydrocarbyl group refers to hydrocarbyl moieties which are substitutedwith at least one atom other than carbon, including moieties in which acarbon chain atom is substituted with a heteroatom such as nitrogen,oxygen, silicon, phosphorous, boron, or a halogen atom, and moieties inwhich the carbon chain comprises additional substituents. Thesesubstituents include alkyl, alkoxy, acyl, acyloxy, alkenyl, alkenoxy,aryl, aryloxy, amino, amido, acetal, carbamyl, carbamate, carbocyclo,cyano, ester, ether, halogen, heterocyclo, hydroxyl, keto, ketal,phospho, nitro, thio, trifluoromethyl, sulfonyl, sulfonamide, and thelike. A lipid may be a phospholipid such as, e.g., phosphatidylethanolamine, phosphatidyl serine, phosphatidyl inositol, cardiolipin,phosphatidyl ethylene glycol, and the like, or a bile acid such ascholic acid. Preferably, a lipid may be a fatty acid, wherein the fattyacid chain comprises an alkyl (saturated) or an alkynyl (unsaturated)group as defined above. Preferred fatty acids include, but are notlimited to, 10,12-pentacosadiynoic acid, hexadecyloctadecanoic acid,cholanic acid, linoleic acid, C24-pentacosadiynoic acid, and palmiticacid. Preferably, a lipid may be palmitic acid or C24-pentacosadiynoicacid.

An exemplary branched polymer may be polyethyleneimine and an exemplarylipid is palmitic acid, C24-pentacosadiynoic acid, or linoleic acid,wherein at least about 40% of the free reactive groups of the polymerare linked to the lipid. An exemplary branched polymer may bepolyethyleneimine and an exemplary lipid is palmitic acid,C24-pentacosadiynoic acid, or linoleic acid, wherein at least about 50%of the free reactive groups of the polymer are linked to the lipid. Anexemplary branched polymer may be polyethyleneimine and an exemplarylipid is palmitic acid, C24-pentacosadiynoic acid, or linoleic acid,wherein at least about 55% of the free reactive groups of the polymerare linked to the lipid. When the branched polymer is polyethyleneimine,the free reactive group is an amine, typically a primary amine and/or asecondary amine.

An exemplary branched polymer may be PAMAM and an exemplary lipid ispalmitic acid, C24-pentacosadiynoic acid, or linoleic acid, wherein atleast about 10% of the free reactive groups of the polymer are linked tothe lipid. An exemplary branched polymer may be PAMAM and an exemplarylipid is palmitic acid, C24-pentacosadiynoic acid, or linoleic acid,wherein at least about 20% of the free reactive groups of the polymerare linked to the lipid. An exemplary branched polymer may be PAMAM andan exemplary lipid is palmitic acid, C24-pentacosadiynoic acid, orlinoleic acid, wherein at least about 30% of the free reactive groups ofthe polymer are linked to the lipid. When the branched polymer is PAMAM,the free reactive group is an amine, typically a primary amine.

(c) Aqueous Core

Nanoparticles comprise an aqueous core. The aqueous core may comprisewater, a buffer solution, a saline solution, a serum solution, andcombinations thereof. The aqueous core may also comprise a biologicallyactive agent, an imaging agent, a metal atom, a therapeutic agent, anoxygen-carrying agent, an allosteric effector, a reducing agent, orcombinations thereof, as detailed below. Preferably, the aqueous corecomprises an oxygen-carrying agent, an allosteric effector, and areducing agent.

(d) Intra-Molecular Cross-Linking of the Particle Exterior

The exterior of the nanoparticle comprises the outer layer of the shell.The outer layer of the shell is intra-molecularly cross-linked in orderto neutralize the surface reactive groups. Stated another way, the outerlayer of the shell is intra-molecularly cross-linked such that thenanoparticle has a near neutral surface. The degree of cross-linkingneeded to achieve a near neutral surface will vary depending upon theamphiphilic polymer. Nanoparticles with a zeta potential of about −15 toabout +15 mV are considered approximately neutral. A nanoparticle with anear neutral surface may have a zeta potential between −15, −14, −13,−12, −11, −10, −9, −7, −6, −5, −4, −3, −2, −1, 0, +1, +2, +3, +4, +5,+6, +7, +8, +9, +10, +11, +12, +13, +14, or +15 mV. A nanoparticle witha near neutral surface may also have a zeta potential of about −15 toabout 0 mV, about −10 to about 0 mV, about −10 to about −5 mV, about −9to about −4 mV, about −8 to about −3 mV, about −7 to about −2 mV, about−6 to about −1 mV, or about −5 to about 0 mV. Alternatively, ananoparticle with a near neutral surface may also have a zeta potentialof about 0 to about +15 mV, about 0 to about +10 mV, about +5 to about+10 mV, about +4 to about +9 mV, about +3 to about +8 mV, about +2 toabout +7 mV, about +1 to about +6 mV, or about 0 to about +5 mV. Zetapotential can affect a nanoparticle's tendency to interact withproteins, microparticles, cells and other biomolecules. A near neutralsurface is an important feature of a nanoparticle of the disclosure,since the nanoparticles will be administered to a subject and it isundesirable for the nanoparticle to substantially interact withproteins, cells and other particles in the blood. Without wishing to bebound by theory, Applicants also believe the degree of cross-linkingsubstantially contains the payload within the interior of the particle,affects the diffusion of gases such as oxygen, carbon dioxide and nitricoxide into or within the nanoparticle. Cross-linking may also impartincreased mechanical stability to nanoparticles, improvebiocompatibility and/or extend circulation longevity. Cross-linking mayalso inhibit oxidative damage to an oxygen-carrying agent.

Surface lipids of the amphiphilic polymer of the outer shell may becross-linked by chemical means. Alternatively, a core polymer of theamphiphilic polymer may be cross-linked by photo-chemical means.Generally, at least about 30% of the available reactive groups of anamphiphilic polymer may be cross-linked, more than 30%, 40%, 50%, 60%,70%, 80%, 90%, or 95% of the available reactive groups of theamphiphilic polymer may be cross-linked. Suitable means of cross-linkingare detailed below in Section II. The degree of cross-linking may bedetermined by any method known in the art.

Preferably, the particle surface is intramolecularly cross-linked with abifunctional linker, such that at least about 30% of the surfacereactive groups of the amphiphilic polymer may be cross-linked,including about 30% to about 50%, about 50% to about 70%, or about 70%to about 100%. Preferred bifunctional linkers include, but are notlimited to, activated (or functionalized) short PEG chains.Alternatively, coupling agents may be used. Short PEG chains maycomprise about 1, 2, 3, 4, 5, or about 6 ethylene oxide monomers.Preferably, short PEG chains comprise 1 to 3 ethylene oxide monomers, ormore preferably, 2 ethylene oxide monomers. Exemplary bifunctionallinkers may include ethylene glycol bis(sulfosuccinimidylsuccinate)(Sulfo-EGS), epoxides, tosylates or chloroformates. Further details areprovided below in Section II.

(e) Optional Pegylation

Additionally, an amphiphilic polymer of a nanoparticle may bederivatized with polyethylene glycol (PEG), as detailed below in SectionII. Preferably, a nanoparticle is derivatized using short PEG chains.Short PEG chains may comprise about 1, 2, 3, 4, 5, or about 6 ethyleneoxide monomers. Preferably, short PEG chains comprise 1 to 3 ethyleneoxide monomers, or more preferably, 2 ethylene oxide monomers.

(f) Payload

A nanoparticle of the disclosure comprises a payload, the payloadcomprising an oxygen-carrying agent, an allosteric effector, and areducing agent. The payload is contained in the interior of thenanoparticle. An oxygen-carrying agent, an allosteric effector, and areducing agent of an oxygen-carrying nanoparticle may be containedwithin the aqueous core of the nanoparticle, may be within thehydrophilic region of the inner layer comprising the shell of thenanoparticle, may be within the hydrophobic region comprising the shellof the nanoparticle, or a combination thereof. It is also envisionedthat an oxygen-carrying agent, an allosteric effector, and a reducingagent may be localized to different locations of a nanoparticle.

i. Oxygen-Carrying Agent

A nanoparticle of the disclosure comprises an oxygen-carrying agent. Anymolecule capable of carrying oxygen may be suitable for use as anoxygen-carrying agent. Non limiting examples of oxygen-carrying agentsinclude perfluorocarbon-based oxygen carriers (PFBOC), hemoglobin-basedoxygen carriers (HBOC), hemoglobin-like oxygen carriers such asleghemoglobin, and artificial hemoglobin-based oxygen carriers such ashemin. As such, an oxygen-carrying agent may be a hemoglobin-basedoxygen carrier (HBOC), a hemoglobin-like oxygen carrier, a PFBOC, or anartificial hemoglobin-based oxygen carrier.

Nanoparticles may comprise about 2000 to about 10,000 oxygen-carryingagent molecules per nanoparticle. Nanoparticles may comprise about 2000,2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000,8500, 9000, 9500, or about 10,000 oxygen-carrying agent molecules pernanoparticle. Nanoparticles may also comprise more than about 10,000oxygen-carrying agent molecules per nanoparticle. The absolute number ofoxygen-carrying agent molecules per nanoparticle can and will varydepending on the size of the nanoparticle, affinity of theoxygen-carrying agent for oxygen, and ability to limit auto-oxidationformation during O₂ offloading.

About 20% to about 60% (w/v) of a nanoparticle of the disclosure maycomprise an oxygen-carrying agent. For example, 20%, 21%, 22%, 23%, 24%,25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%,39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%,53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60% (w/v) of a nanoparticle maycomprise an oxygen-carrying agent. Alternatively, about 20%, 25%, 30%,35%, 40%, 45%, 50%, 55%, or about 60% (w/v) of a nanoparticle comprisesan oxygen-carrying agent. Preferably, about 25% to about 60%, about 30%to about 60%, about 35% to about 60%, about 40% to about 60%, about 45%to about 60%, about 50% to about 60% (w/v) of a nanoparticle comprisesan oxygen-carrying agent.

Preferably, an oxygen-carrying agent is an artificial hemoglobin-basedoxygen carrier such as hemin. Even more preferably, an oxygen-carryingagent is a hemoglobin-based oxygen carrier. Hemoglobin is aniron-containing oxygen transport metalloprotein, and is the maincomponent of red blood cells, comprising about 33% of the cell mass.Each molecule of hemoglobin has 4 subunits, two α chains and two βchains, which are arranged in a tetrameric structure. Each subunit alsocontains one heme group, which is the iron-containing center that bindsoxygen. As such, each hemoglobin molecule can bind four oxygenmolecules.

The present disclosure is not limited by the source of hemoglobin. Theterm “hemoglobin” refers to naturally occurring or synthetic hemoglobin.For example, a hemoglobin-based oxygen-carrying agent of the disclosuremay be from animals. Alternatively, a hemoglobin-based oxygen-carryingagent of the disclosure may be from humans. Preferred sources ofhemoglobin are humans, cows and pigs.

A hemoglobin oxygen-based carrying agent may be isolated and purifiedfrom a human or animals such as cows and pigs. Alternatively, ahemoglobin-based oxygen-carrying agent may be produced by chemicalsynthesis and recombinant techniques. Human α- and β-globin genes haveboth been cloned and sequenced (See for example, Liebhaber et al.,P.N.A.S. 77: 7054-7058 (1980); Marotta et al., J. Biol. Chem. 353:5040-5053 (1977) (beta-globin cDNA).

It will be appreciated by those skilled in the art that hemoglobin aminoacid sequence polymorphisms may exist within a population (e.g., thehuman, cow or pig population). Such genetic polymorphism may exist amongindividuals within a population due to natural allelic variation. Anyand all such amino acid variations and resulting polymorphisms that arethe result of natural allelic variation and that do not alter thefunctional activity of hemoglobin are intended to be within the scope ofthe disclosure. Similarly, the term hemoglobin oxygen-based carryingagent includes hemoglobin that have been engineered to adjust the oxygenbinding and release properties of hemoglobin when used as anoxygen-carrying agent in an oxygen-carrying nanoparticle (See, e.g.,Nagai, et al., (1985) P.N.A.S., 82: 7252-7255, and U.S. Pat. No.5,028,588). A hemoglobin oxygen-based carrying agent may also benaturally occurring hemoglobin, chimeric hemoglobin, recombinanthemoglobin, hemoglobin fragments, or hemoglobin comprising combinationsthereof without departing from the scope of the disclosure.

A hemoglobin oxygen-based carrying agent may be either native orsubsequently modified by a chemical reaction such as intra- orinter-molecular cross-linking, polymerization, or the addition ofchemical groups such as polyalkylene oxides or other adducts.Representative examples of modified hemoglobin oxygen-carrying agentsare disclosed in a number of issued United States patents, includingU.S. Pat. No. 4,857,636, U.S. Pat. No. 4,600,531, U.S. Pat. No.4,061,736, U.S. Pat. No. 3,925,344, U.S. Pat. No. 4,529,719, U.S. Pat.No. 4,473,496, U.S. Pat. No. 4,584,130, U.S. Pat. No. 5,250,665, U.S.Pat. No. 4,826,811, and U.S. Pat. No. 5,194,590.

Preferably, an oxygen-carrying agent is hemoglobin isolated from humans,cows, or pigs. Even more preferably, an oxygen-carrying agent ishemoglobin isolated from humans. Methods of isolating hemoglobin from asubject are known in the art and may be as described in the examples andin Rogers et al., 2009, FASEB Journal 23:3159-3170, the disclosure ofwhich is incorporated herein in its entirety. Alternative methods forisolating hemoglobin are also known in the art. For example, hemoglobinmay be purified from a donor using tangential flow filtration. See, forexample, Elmer et al., 2011, Journal of chromatography B, Analyticaltechnologies in the biomedical and life sciences, 879:1311-138, and/orPalmer et al., 2009, Biotechnol. Prog., 25:189-199. Irrespective of thesource of hemoglobin, a hemoglobin oxygen-carrying agent issubstantially pure, and free of stroma and endotoxin.

Nanoparticles may comprise about 2000 to about 10,000 hemoglobinmolecules per nanoparticle. Nanoparticles may comprise about 2000, 2500,3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500,9000, 9500, or about 10,000 hemoglobin molecules per nanoparticle ormore. A nanoparticle may comprise about 2000 to about 6000 hemoglobinmolecules per nanoparticle or about 6000 to about 10000 hemoglobinmolecules per nanoparticle. A nanoparticle may also comprise about 3000to about 6000 hemoglobin molecules per nanoparticle, about 4000 to about7000 hemoglobin molecules per nanoparticle, about 5000 to about 8000hemoglobin molecules per nanoparticle, about 6000 to about 9000hemoglobin molecules per nanoparticle, or about 7000 to about 10,000hemoglobin molecules per nanoparticle. Alternatively, a nanoparticle maycomprise about 3000 to about 4000 hemoglobin molecules per nanoparticle,about 4000 to about 5000 hemoglobin molecules per nanoparticle, about5000 to about 6000 hemoglobin molecules per nanoparticle, about 6000 toabout 7000 hemoglobin molecules per nanoparticle, about 7000 to about8000 hemoglobin molecules per nanoparticle, about 8000 to about 9000hemoglobin molecules per nanoparticle, or about 9000 to about 10,000hemoglobin molecules per nanoparticle. The absolute number of hemoglobinmolecules per nanoparticle can and will vary depending on the size ofthe nanoparticle.

Generally, about 20% to about 60% (w/v) of a nanoparticle may comprisehemoglobin. For example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%,29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%,43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%,57%, 58%, 59%, or 60% (w/v) of a nanoparticle may comprise hemoglobin.Alternatively, about 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or about60% (w/v) of a nanoparticle comprises hemoglobin. Preferably, about 25%to about 60%, about 30% to about 60%, about 35% to about 60%, about 40%to about 60%, about 45% to about 60%, about 50% to about 60% (w/v) of ananoparticle comprises hemoglobin. While not wishing to be bound bytheory, it is believed that the high concentration of hemoglobin maystabilize hemoglobin, and prevent concentration-dependent hemoglobintetramer dissociation into individual α and β dimmers.

If the hemoglobin concentration of an oxygen-carrying nanoparticlecannot be determined directly, as described herein, it may be estimatedfrom the iron content of the nanoparticle. The iron content ofhemoglobin is known in the art. See, for example, Bernhart FW and SkeggsL 1943 J Biol Chem 147:19-22.

ii. Allosteric Effector

A nanoparticle of the disclosure comprises an allosteric effector thatmodulates the affinity of an oxygen-carrying agent to oxygen, andmodulates the rate or amount of oxygen binding to, or releasing from, anoxygen-carrying agent in a nanoparticle. An allosteric effector mayincrease the offload of oxygen from an oxygen carrier to a tissue orcell that is deoxygenated within a subject, and/or increase loading ofoxygen onto an oxygen carrier from an oxygenated tissue such as lungs.As such, an allosteric effector may allow oxygen to be bound in thelungs and released in the tissues within the narrow physiological rangeof partial oxygen pressures from 40-100 mmHg in the deoxygenated tissuesand in oxygen-rich lungs. Facile control of O₂ affinity is essential tothe design of a robust oxygen-carrying nanoparticle, affording abilityto tailor nanoparticle design to clinical context. For example, theability to modulate O₂ affinity allows the design of a nanoparticle withincreasing O₂ affinity suitable for treatment of hypoxia at highaltitude, and the design of a nanoparticle with decreasing O₂ affinitysuitable for treatment of hypoxia at sea level.

A nanoparticle may comprise one allosteric effector or a combination ofmore than one allosteric effector. Non limiting examples of allostericeffectors capable of modulating the affinity of hemoglobin to oxygeninclude 2,3-diphosphoglycerate (2,3-DPG) (also known as2,3-bisphosphoglyceric acid or 2,3-BPG) or an isomer derived therefrom,inositol hexaphosphate (IHP), pyridoxal-phosphate (PLP), or RSR-4,RSR-13(2-[4-[[(3,5-dimethylanilinocarbonyl]methyl]-phenoxy]-2-methylpropionic acid), the structure ofwhich is depicted below.

The concentration of allosteric effector in an oxygen-carryingnanoparticle can and will vary, and may be determined experimentally tooptimize the oxygen binding and release dynamics of a nanoparticle asdescribed herein. The concentration of 2,3-DPG may be described in termsof a molar ratio to oxygen-carrying agent. The molar ratio of allostericeffector to oxygen-carrying agent may be about 0.20, 0.25, 0.30, 0.35,0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95,1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55,1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95, 1.00, 1.05, 1.10, 1.15,1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75,1.80, 1.85, 1.90, 1.95, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.35,2.40, 2.45, 2.50, 2.55, 2.60, 2.65, 2.70, 2.75, 2.80, 2.85, 2.90, 2.95,3.00, 3.05, 3.10, 3.15, 3.20, 3.25, 3.30, 3.35, 3.40, 3.45, 3.50, 3.55,3.60, 3.65, 3.70, 3.75, 3.80, 3.85, 3.90, 3.95, 4.00, 4.05, 4.10, 4.15,4.20, 4.25, 4.30, 4.35, 4.40, 4.45, 4.50, 4.55, 4.60, 4.65, 4.70, 4.75,4.80, 4.85, 4.90, 4.95, 5.00, 5.05, 5.10, 5.15, 5.20, 5.25, 5.30, 5.35,5.40, 5.45, 5.50, 5.55, 5.60, 5.65, 5.70, 5.75, 5.80, 5.85, 5.90, 5.95,6.00, 6.05, 6.10, 6.15, 6.20, 6.25, 6.30, 6.35, 6.40, 6.45, 6.50, 6.55,6.60, 6.65, 6.70, 6.75, 6.80, 6.85, 6.90, 6.95, 7.00, 7.05, 7.10, 7.15,7.20, 7.25, 7.30, 7.35, 7.40, 7.45, 7.50, 7.55, 7.60, 7.65, 7.70, 7.75,7.80, 7.85, 7.90, 7.95, 8.00, 8.05, 8.10, 8.15, 8.20, 8.25, 8.30, 8.35,8.40, 8.45, 8.50, 8.55, 8.60, 8.65, 8.70, 8.75, 8.80, 8.85, 8.90, 8.95,9.00, 9.05, 9.10, 9.15, 9.20, 9.25, 9.30, 9.35, 9.40, 9.45, 9.50, 9.55,9.60, 9.65, 9.70, 9.75, 9.80, 9.85, 9.90, 9.95, or about 10.00.

Preferably, an allosteric effector is 2,3-DPG. 2,3-DPG may modulate theaffinity of an oxygen-carrying agent to oxygen by enhancingresponsiveness of an oxygen-carrying nanoparticle to pH. 2.3-DPG may besynthesized by any method known in the art, including chemical synthesisor enzymatic synthesis. See for example, Baer E. “A synthesis of2,3-diphospho-d-glyceric aid.” J Biol Chem. 1950; 185:763-767; orGrisolia S, Joyce BK. “Enzymatic synthesis and isolation of2,3-diphosphoglycerate.” J Biol Chem. 1958; 233: 18-19, each herebyincorporated by reference in its entirety. Synthesis may be confirmed byMS and/or NMR.

The concentration of 2,3-DPG in an oxygen-carrying nanoparticle can andwill vary, and may be determined experimentally to optimize the oxygenbinding and release dynamics of a nanoparticle as described herein. Whenan oxygen-carrying agent is hemoglobin, the concentration of 2,3-DPG maybe about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3,1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or about 2 mg/mg hemoglobin. Preferably,the concentration of 2,3-DPG may be about 0.7, 0.8, 0.9, 1, 1.1, 1.2, orabout 1.3 mg/mg hemoglobin. Alternatively, the concentration of 2,3-DPGmay be described in terms of a molar ratio to hemoglobin. When anoxygen-carrying agent is hemoglobin, the molar ratio of a 2,3-DPG tohemoglobin may be about 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55,0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15,1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75,1.80, 1.85, 1.90, 1.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35,1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95,2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, 2.45, 2.50, 2.55,2.60, 2.65, 2.70, 2.75, 2.80, 2.85, 2.90, 2.95, 3.00, 3.05, 3.10, 3.15,3.20, 3.25, 3.30, 3.35, 3.40, 3.45, 3.50, 3.55, 3.60, 3.65, 3.70, 3.75,3.80, 3.85, 3.90, 3.95, 4.00, 4.05, 4.10, 4.15, 4.20, 4.25, 4.30, 4.35,4.40, 4.45, 4.50, 4.55, 4.60, 4.65, 4.70, 4.75, 4.80, 4.85, 4.90, 4.95,5.00, 5.05, 5.10, 5.15, 5.20, 5.25, 5.30, 5.35, 5.40, 5.45, 5.50, 5.55,5.60, 5.65, 5.70, 5.75, 5.80, 5.85, 5.90, 5.95, 6.00, 6.05, 6.10, 6.15,6.20, 6.25, 6.30, 6.35, 6.40, 6.45, 6.50, 6.55, 6.60, 6.65, 6.70, 6.75,6.80, 6.85, 6.90, 6.95, 7.00, 7.05, 7.10, 7.15, 7.20, 7.25, 7.30, 7.35,7.40, 7.45, 7.50, 7.55, 7.60, 7.65, 7.70, 7.75, 7.80, 7.85, 7.90, 7.95,8.00, 8.05, 8.10, 8.15, 8.20, 8.25, 8.30, 8.35, 8.40, 8.45, 8.50, 8.55,8.60, 8.65, 8.70, 8.75, 8.80, 8.85, 8.90, 8.95, 9.00, 9.05, 9.10, 9.15,9.20, 9.25, 9.30, 9.35, 9.40, 9.45, 9.50, 9.55, 9.60, 9.65, 9.70, 9.75,9.80, 9.85, 9.90, 9.95, or about 10.00.

iii. Reducing Agent

A nanoparticle of the disclosure comprises a reducing agent. When anoxygen-carrying agent is hemoglobin, the hemoglobin may oxidize tomethemoglobin, in which the iron in the heme group is in theFe³⁺(ferric) state, not the Fe²⁺(ferrous) of normal hemoglobin.Oxidation of hemoglobin to methemoglobin reduces the affinity ofhemoglobin to oxygen and reduces the oxygen-carrying capacity ofnanoparticles over time. A reducing agent may prevent oxidation ofhemoglobin, regenerate oxidized hemoglobin, or a combination of both. Itis contemplated within the scope of this invention that a reducing mayprevent oxidation of any oxygen-carrying agents comprising heme. Assuch, a reducing agent may be capable of maintaining and extending theoxygen-carrying functionality of nanoparticles over a longer period oftime, compared to when a reducing agent is not present.

A nanoparticle may comprise one reducing agent or a combination of morethan one allosteric effector. Non limiting examples of reducing agentssuitable for regenerating oxidized hemoglobin include leucomethyleneblue, and derivatives thereof, such as leucobenzyl methylene blue, aswell as glutathionine and ascorbate. The concentration of a reducingagent may be sufficient to limit methemoglobin concentrations in ananoparticle to no more than about 1%, 5%, 6%, 7%, 8%, 9%, 10%, 11%,12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or less of the totalconcentration of hemoglobin in nanoparticles. Preferably, theconcentration of a reducing agent is sufficient to limit methemoglobinconcentrations in a nanoparticle to no more than about 8%, 9%, 10%, 11%,12%, 13%, 14%, or about 15% or less of the total concentration ofhemoglobin in nanoparticles. When an oxygen-carrying agent ishemoglobin, the concentration of a reducing agent may be about 0.1, 0.2,0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,1.8, 1.9, or about 2 mg/mg hemoglobin. Preferably, the concentration ofa reducing agent may be about 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or about 0.8mg/mg hemoglobin. Alternatively, the concentration of reducing agent maybe described in terms of a molar ratio to hemoglobin. When anoxygen-carrying agent is hemoglobin, the molar ratio of a reducing agentto hemoglobin may be about 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50,0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10,1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70,1.75, 1.80, 1.85, 1.90, 1.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30,1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90,1.95, 2.00, 2.05, 2.10, 2.15, 2.20, 2.25, 2.30, 2.35, 2.40, 2.45, 2.50,2.55, 2.60, 2.65, 2.70, 2.75, 2.80, 2.85, 2.90, 2.95, 3.00, 3.05, 3.10,3.15, 3.20, 3.25, 3.30, 3.35, 3.40, 3.45, 3.50, 3.55, 3.60, 3.65, 3.70,3.75, 3.80, 3.85, 3.90, 3.95, 4.00, 4.05, 4.10, 4.15, 4.20, 4.25, 4.30,4.35, 4.40, 4.45, 4.50, 4.55, 4.60, 4.65, 4.70, 4.75, 4.80, 4.85, 4.90,4.95, 5.00, 5.05, 5.10, 5.15, 5.20, 5.25, 5.30, 5.35, 5.40, 5.45, 5.50,5.55, 5.60, 5.65, 5.70, 5.75, 5.80, 5.85, 5.90, 5.95, 6.00, 6.05, 6.10,6.15, 6.20, 6.25, 6.30, 6.35, 6.40, 6.45, 6.50, 6.55, 6.60, 6.65, 6.70,6.75, 6.80, 6.85, 6.90, 6.95, 7.00, 7.05, 7.10, 7.15, 7.20, 7.25, 7.30,7.35, 7.40, 7.45, 7.50, 7.55, 7.60, 7.65, 7.70, 7.75, 7.80, 7.85, 7.90,7.95, 8.00, 8.05, 8.10, 8.15, 8.20, 8.25, 8.30, 8.35, 8.40, 8.45, 8.50,8.55, 8.60, 8.65, 8.70, 8.75, 8.80, 8.85, 8.90, 8.95, 9.00, 9.05, 9.10,9.15, 9.20, 9.25, 9.30, 9.35, 9.40, 9.45, 9.50, 9.55, 9.60, 9.65, 9.70,9.75, 9.80, 9.85, 9.90, 9.95, or about 10.00.

iv. Tuning Oxygen-Carrying Nanoparticles

An important feature of a nanoparticle of the disclosure is thephysiologic linkage between particle O₂ affinity and tissue respiration.While conventional blood substitutes known in the art increase arterialO₂ content, the appropriate release of O₂ (i.e. along a physiological O₂dissociation curve) by these blood substitutes is infrequently achievedin vivo, due to lack of normal allosteric control of Hb˜O₂ affinity(expressed as p50, the p O₂ at which hemoglobin saturation with O₂ (SHbO₂) is 50%). The present invention solves this problem with theinnovative design of an allosteric effector shuttle-reservoir. Toillustrate how the structure of the nanoparticle influences itsfunction, consider a particle comprising hemoglobin as an exemplaryoxygen-carrying agent, 2,3-DPG as an exemplary allosteric effector andpolyethyleneimine (PEI) as an exemplary branched polymer. Thenanoparticle payload contains a heterotropic allosteric effectormolecule (2,3-DPG), which modifies Hb O₂ affinity; the freeconcentration of 2,3-DPG in the particle core is modulated bypH-responsive binding to the nanoparticle inner shell—so that 2,3,-DPGis sequestered to the shell during lung perfusion (at high pH, therebyincreasing HbO₂ affinity and facilitating O₂ capture) and 2,3-DPG isreleased from the shell during systemic perfusion (low pH, therebylowering HbO₂ affinity and facilitating O₂ release). This effect isamplified in settings of physiologic need [with lung pathology,hyperventilation raises pH and enhances O₂ capture; with tissue hypoxia,anaerobic metabolism lowers pH and enhances O₂ release]. As circulatorytransit is completed in the lung (or, as hypoxia abates) and pH rises,2,3-DPG will increasingly re-associate with the shell, thereby: 1)facilitating O₂ loading in the lung and 2) linking p50 to tissue O₂ debtand its resolution. This physiologically responsive allosteric effectorreservoir-shuttle meaningfully differentiates oxygen-carryingnanoparticles of the disclosure from all HBOC designs. Moreover, thedesign of an oxygen-carrying nanoparticle of the disclosure allowsaspects of this shuttle to be refined or “tuned”, affording ability totailor nanoparticle design to clinical context.

Nanoparticles of the disclosure may be tuned to mimic theoxygen-carrying characteristics of red blood cells. Those skilled in theart will appreciate that the oxygen-carrying characteristics of redblood cells may be described by the oxygen-hemoglobin dissociation curveof hemoglobin. The oxygen-hemoglobin dissociation curve plots oxygensaturation (sO₂) against partial pressure of oxygen in the blood (pO₂),and describes the affinity of hemoglobin for oxygen under physiologicalconditions of pO₂, partial pressure of CO₂ (pCO₂), pH, temperature, andconcentration of allosteric effectors, among other factors. As such,nanoparticles may be tuned to substantially mimic the oxygen-hemoglobindissociation curve of hemoglobin.

Nanoparticles may be tuned to generate nanoparticles with 50% saturationof the oxygen-carrying agent (p50) of about 10, 15, 20, 25, 30, 35 orabout 40 mmHg or more. Preferably, oxygen-carrying nanoparticles aretuned to generate nanoparticles with p50 of about 20 mmHg, 25 mmHg, orabout 30 mmHg. Also preferably, oxygen-carrying nanoparticles are tunedto generate nanoparticles with p50 of about 26 mmHg. Methods of tuningp50 of nanoparticles may include tuning the morphology of nanoparticlesto increase or decrease the surface area of nanoparticles, tuning theconcentration of an oxygen-carrying agent such as hemoglobin in ananoparticle, tuning the concentration of a reducing agent to limitoxidation of hemoglobin in a nanoparticle, tuning the outer shell of ananoparticle to control oxygen diffusion into and out of nanoparticles,or combinations thereof.

Nanoparticles may be tuned to enhance the responsiveness of anoxygen-carrying nanoparticle to pH. Responsiveness of hemoglobin to pH,also called the Bohr effect, allows more efficient oxygen binding in thehigh pH environment of the lungs, and more efficient release of oxygenin the low pH environment of deoxygenated tissue. Methods of enhance theresponsiveness of a nanoparticle to pH may include tuning theconcentration of an allosteric effector of a nanoparticle. Such anallosteric effector may be 2,3-DPG.

Nanoparticles may be tuned to limit oxidation of hemoglobin tomethemoglobin. As described above, nanoparticles may be tuned to limitmethemoglobin concentrations in a nanoparticle to no more than about 1%,5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%,20% or less of the total concentration of hemoglobin in nanoparticles.Preferably, oxygen-carrying nanoparticles are tuned to limitmethemoglobin concentrations in a nanoparticle to no more than about 8%,9%, 10%, 11%, 12%, 13%, 14% or about 15% or less of the totalconcentration of hemoglobin in nanoparticles. Methods of tuningoxidation of hemoglobin may include tuning the morphology ofnanoparticles to increase or decrease the surface area of nanoparticles,tuning the concentration of a reducing agent of a nanoparticle, andcombinations thereof. Preferably, oxidation of hemoglobin may be tunedby tuning the concentration of a reducing agent such as leucomethyleneblue or leucobenzyl methylene blue.

Nanoparticles may also be tuned to limit NO scavenging. NO is animportant cellular signaling molecule in mammals and is involved in manyphysiological and pathological processes. In addition, NO is a powerfulvasodilator. Hemoglobin binds NO with an avidity that parallels thebinding avidity of hemoglobin to oxygen. Left uncontrolled, a hemoglobinbased oxygen carrier may sequester NO, and may lead to vasoconstriction.Methods of tuning oxygen-carrying nanoparticles of the disclosure tolimit NO scavenging may include tuning the morphology of nanoparticlesto increase or decrease the surface area of nanoparticles exposed tooxygen and NO, tuning the outer shell of a nanoparticle to control NOdiffusion into nanoparticles, tuning overall particle size, tuningpayload density, or combinations thereof. Those skilled in the art willappreciate that nanoparticles may be tuned to limit NO diffusion into ananoparticle, but permit oxygen diffusion for oxygen transport. Forexample, the degree of outer layer cross-linking can be varied tomodulate the extent and rate of NO sequestration by the nanoparticle.

Methods of tuning the shell of a nanoparticle may include tuningcomponent ratios of the shell, tuning cross-linking of components of theshell, and tuning pegylation of the shell of nanoparticles. Componentsof the shell, cross-linking of components of the shell, and pegylationof the shell of nanoparticles may be as described above. Preferably, theshell of a nanoparticle may be tuned by increasing or decreasing thethickness of the shell, increasing or decreasing the hydrophobicity orhydrophilicity of the shell, and increasing or decreasing the level ofcrosslinking or pegylation of the shell. Further details are provided inthe Examples.

(g) Optional Molecules

Bi-concaved disc shaped oxygen-carrying nanoparticles may furthercomprise at least one molecule selected from the group consisting of atargeting moiety, a biologically active agent, an imaging agent, a metalatom, and a therapeutic agent. A molecule may be water soluble or waterinsoluble. A molecule may be contained within the aqueous inner core ofthe nanoparticle, may be conjugated to the surface of the amphiphilicpolymer comprising the outer shell of the nanoparticle, may beconjugated within a hydrophilic region of an amphiphilic polymercomprising the outer shell of a nanoparticle, or may be conjugatedwithin a hydrophobic region of an amphiphilic polymer comprising theouter shell of the nanoparticle. It is also envisioned that innanoparticles comprising more than one optional molecule, molecules maybe localized to different locations of the nanoparticle. In general, atargeting moiety will be conjugated to the surface of an amphiphilicpolymer comprising the outer shell of the nanoparticle. As used herein,the term “conjugation” refers to either covalent or non-covalent means.Non-covalent means may include ionic bonding, dative bonding, hydrogenbonding, metallic bonding, and so forth, as well as electrostatic,hydrophobic, and van der Waals interactions.

i. Metal Atoms

A variety of metal atoms are suitable for inclusion in nanoparticles. Ametal atom may generally be selected from the group of metal atomscomprised of metals with an atomic number of twenty or greater. Forinstance, metal atoms may be calcium atoms, scandium atoms, titaniumatoms, vanadium atoms, chromium atoms, manganese atoms, iron atoms,cobalt atoms, nickel atoms, copper atoms, zinc atoms, gallium atoms,germanium atoms, arsenic atoms, selenium atoms, bromine atoms, kryptonatoms, rubidium atoms, strontium atoms, yttrium atoms, zirconium atoms,niobium atoms, molybdenum atoms, technetium atoms, ruthenium atoms,rhodium atoms, palladium atoms, silver atoms, cadmium atoms, indiumatoms, tin atoms, antimony atoms, tellurium atoms, iodine atoms, xenonatoms, cesium atoms, barium atoms, lanthanum atoms, hafnium atoms,tantalum atoms, tungsten atoms, rhenium atoms, osmium atoms, iridiumatoms, platinum atoms, gold atoms, mercury atoms, thallium atoms, leadatoms, bismuth atoms, francium atoms, radium atoms, actinium atoms,cerium atoms, praseodymium atoms, neodymium atoms, promethium atoms,samarium atoms, europium atoms, gadolinium atoms, terbium atoms,dysprosium atoms, holmium atoms, erbium atoms, thulium atoms, ytterbiumatoms, lutetium atoms, thorium atoms, protactinium atoms, uranium atoms,neptunium atoms, plutonium atoms, americium atoms, curium atoms,berkelium atoms, californium atoms, einsteinium atoms, fermium atoms,mendelevium atoms, nobelium atoms, or lawrencium atoms.

Metal atoms comprising a nanoparticle may be metal ions. Metal atoms maybe in the form of +1, +2, or +3 oxidation states. For instance,non-limiting examples include Ba²⁺, Bi³⁺, Cs⁺, Ca²⁺, Cr²⁺, Cr³⁺, Cr⁶⁺,Co²⁺, Co³⁺, Cu⁺, Cu²⁺, Cu³⁺, Ga³⁺, Gd³⁺, Au⁺, Au³⁺, Fe²⁺, Fe³⁺, Pb²⁺,Pb⁴⁺, Mn²⁺, Mn³⁺, Mn⁴⁺, Mn⁷⁺, Hg²⁺, Ni²⁺, Ni³⁺, Ag⁺, Sr²⁺, Sn²⁺, Sn⁴⁺,and Zn²⁺. Metal ions may comprise metal complexes, compounds, orchelates. For example, metal atoms may comprise a complex, chelate, orcompound with porphyrin, diethylene triamine pentaacetic acid (DTPA), ortetramethyl heptanedionate (TMHD), 2,4-pentanedione,1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA),ethylenediamine-tetraacetic acid disodium salt (EDTA),ethyleneglycol-O,O′-bis(2-aminoethyl)-N,N,N′,N′-tetraacetic acid (EGTA),N-(2-hydroxyethyl)ethylenediamine-N, N′, N′-triacetic acid trisodiumsalt (HEDTA), nitrilotriacetic acid (NTA), and1,4,8,11-tetraazacyclotetradecane-N,N′,N″,N′″-tetraacetic acid (TETA).Metal complexes, compounds, or chelates may be organo soluble or watersoluble. Non-limiting examples of suitable organo soluble complexesinclude pentanedione-gadolinium (III), bismuthneodecanoate, iohexol andrelated compounds, and organo soluble complexes of gold. Exemplary watersoluble metal chelates or complexes include, but are not limited to,Mn-DTPA, Mn-porphyrin, and Gd-DTPA.

Metal atoms may comprise a metal oxide. For instance, non-limitingexamples of metal oxides may include iron oxide, manganese oxide, orgadolinium oxide. Additional examples may include magnetite, maghemite,or a combination thereof. A metal oxide may have the formula MFe₂O₄,where M is selected from the group comprising Fe, Mn, Co, Ni, Mg, Cu,Zn, Ba, Sr or a combination thereof. A metal oxide may be magnetic.Preferably, a metal atom may comprise iron oxide. A nanoparticle mayalso comprise both a metal oxide and an additional metal as describedherein. For instance, a nanoparticle may comprise a metal oxide and anadditional metal such as iodine, gadolinium, bismuth, or gold. Generallyspeaking, a metal oxide included in a nanoparticle is between about 1and about 30 nm in diameter. For example, a metal oxide may be about 1,2, 3, 4, 5, 10, 15, 20, 25, or 30 nm in diameter.

Typically, a nanoparticle comprises at least 50,000 metal atoms. Ananoparticle may comprise at least 100,000, at least 150,000, at least200,000, at least 250,000, at least 300,000, at least 350,000, or atleast 400,000 metal atoms.

ii. Biologically Active Agent

Oxygen binding nanoparticles may also further comprise at least onebiologically active agent in addition to an oxygen-carryingnanoparticle. Non-limiting examples of suitable biologically activeagents include pharmaceuticals, therapeutic agents, diagnostic agents,radioactive isotopes, genetic materials, proteins, carbohydrates,lipids, nucleic acid based materials, and combinations thereof. Abiologically active agent may be in its native form or it may bederivatized with hydrophobic or charged moieties to enhanceincorporation or adsorption to a nanoparticle. Accordingly, abiologically active agent may be water soluble or water insoluble. Asdetailed above, a biologically active may be contained within theaqueous inner core, conjugated to the surface of the amphiphilic polymercomprising the outer shell, conjugated within the hydrophilic region ofthe amphiphilic polymer comprising the outer shell, or conjugated withinthe hydrophobic region of the amphiphilic polymer comprising the outershell.

Non-limiting examples of biologically active agents may includeimmune-related agents, thyroid agents, respiratory products,antineoplastic agents, anti-helmintics, anti-malarials, mitoticinhibitors, hormones, anti-protozoans, anti-tuberculars, cardiovascularproducts, blood products, biological response modifiers, anti-fungalagents, vitamins, peptides, anti-allergic agents, anti-coagulationagents, circulatory drugs, metabolic potentiators, anti-virals,anti-anginals, antibiotics, anti-inflammatories, anti-rheumatics,narcotics, cardiac glycosides, neuromuscular blockers, sedatives, localanesthetics, general anesthetics, or radioactive atoms or ions.Additionally, a nanoparticle may comprise two or more, three or more, orfour or more biologically active agents.

The biologically active agent may also be a targeting moiety (seebelow). For instance, an antibody, nucleic acid, peptide fragment, smallorganic molecule, or a mimetic of a biologically active ligand may be atherapeutic agent, such as an antagonist or agonist, when bound tospecific epitopes. Thus, a targeting moiety and a therapeutic agent maybe constituted by a single component which functions both to target ananoparticle and to provide a therapeutic agent to the desired site.

The amount of therapeutic agent incorporated into a nanoparticle willvary. Those of skill in the art will appreciate that the loading ratewill depend upon the type of therapeutic agent and the intended target,for example.

iii. Targeting Moiety

Bi-concaved disc shaped nanoparticles may also comprise a targetingmoiety. A targeting moiety directs or targets the nanoparticle to aparticular site or location. Targeted particles may include a widevariety of targeting moieties conjugated to the surface of the outershell, including, but not limited to, antibodies, antibody fragments,peptides, small molecules, polysaccharides, nucleic acids, aptamers,peptidomimetics, other mimetics, and drugs alone or in combination.Targeting moieties may be utilized to specifically bind thenanoparticles to cellular epitopes and/or receptors. Targeting moietiesmay be conjugated directly or indirectly to a nanoparticle.

Direct conjugation of targeting moieties to a nanoparticle refers to thepreparation of a targeting moiety-nanoparticle complex wherein atargeting moiety is either adsorbed through ionic, electrostatic,hydrophobic or other non-covalent means to the nanoparticle surface(e.g., via an acylated-antibody or hybridization between complementarynucleic acid sequences), or chemically linked to the surface of theouter shell through covalent bonds to a component of the conjugatedlipids, or intrinsically incorporated into the amphiphilic polymer ofthe outer shell (e.g., a lipid derivatized to a peptidomimetic agent). Atargeting moiety also may be directly conjugated to a nanoparticle via alinker molecule. A linker molecule comprises at least two functionalgroups such that the linker molecule is disposed between a nanoparticleand a targeting moiety.

Indirect conjugation refers to forming a complex between a nanoparticleand a targeting moiety in vivo in two or more steps. Indirectconjugation utilizes a chemical linking system to produce the close andspecific apposition of the nanoparticle to a targeted cell or tissuesurface. A non-limiting example of an indirect targeting system isavidin-biotin.

iv. Imaging Agents

Bi-concaved disc shaped nanoparticles may also comprise an imagingagent. An imaging agent may comprise a metal atom, as detailed above, ormay be a radionuclide. Non-limiting examples of suitable radionuclidesinclude technetium-99 m, ilodine-123 and 131, thallium-201, gallium-67,fluorine-18, fluorodeoxyglucose, and indium-111. An imaging agent mayalso be a fluorophore. Suitable fluorophores include, but are notlimited to, fluorescein isothiocyante (FITC), fluoresceinthiosemicarbazide, rhodamime, Texas Red, CyDyes (e.g., Cy3, Cy5, Cy5.5),Alexa Fluors (e.g., Alexa⁴⁸⁸, Alexa⁵⁵⁵, Alexa⁵⁹⁴; Alexa⁶⁴⁷), and nearinfrared (NIR) (700-900 nm) fluorescent dyes.

(h) Preferred Embodiments

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising an oxygen-carryingagent, an allosteric effector and a reducing agent. The payload is inthe interior of the nanoparticle. The amphiphilic polymer comprises abranched amine-containing polymer with reactive groups and is linked toa lipid via the reactive groups, such that at least about 25% of thefree reactive groups are linked to lipids. The surface reactive groupsof the amphiphilic polymer comprising the shell are cross-linked with abifunctional linker. The average diameter of the nanoparticle may befrom about 130 nm to about 300 nm, and the average height of thenanoparticle is from about 30 nm to about 80 nm. The nanoparticle maycomprise a through-hole or a depression. The branched polymer may be apolyethyleneimine branched polymer, a PAMAM dendrimer, a star polymer,or a graft polymer. The lipid may be palmitic acid orC24-pentacosadiynoic acid. The nanoparticle may comprise about 20 toabout 60% (w/v) oxygen-carrying agent molecules. The ratio ofoxygen-carrying agent to allosteric effector and oxygen-carrying agentto reducing agent may be about independently selected from the groupconsisting of 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1,3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1. The nanoparticle designallows the effective release of O₂ during perfusion across the O₂tensions/gradients encountered in normal/abnormal human physiology (e.g.tissue pO₂ range from 40 to 5 Torr). The nanoparticle may notsubstantially sequester nitric oxide. The nanoparticle may limit theoxidation of the oxygen-carrying agent to about 10% or less of the totalconcentration of oxygen-carrying agent in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising an oxygen-carryingagent, an allosteric effector and a reducing agent. The payload is inthe interior of the nanoparticle. The amphiphilic polymer comprises abranched amine-containing polymer with reactive groups and is linked toa lipid via the reactive groups, such that at least about free 40% ofthe reactive groups are linked to lipids. The surface reactive groups ofthe amphiphilic polymer comprising the shell are cross-linked with abifunctional linker. The average diameter of the nanoparticle may befrom about 130 nm to about 300 nm, and the average height of thenanoparticle is from about 30 nm to about 80 nm. The nanoparticle maycomprise a through-hole or a depression. The branched polymer may be apolyethyleneimine branched polymer, a PAMAM dendrimer, a star polymer,or a graft polymer. The lipid may be palmitic acid orC24-pentacosadiynoic acid. The nanoparticle may comprise about 20 toabout 60% (w/v) oxygen-carrying agent molecules. The ratio ofoxygen-carrying agent to allosteric effector and oxygen-carrying agentto reducing agent may be about independently selected from the groupconsisting of 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1,3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1. The nanoparticle designallows the effective release of O₂ during perfusion across the O₂tensions/gradients encountered in normal/abnormal human physiology (e.g.tissue pO₂ range from 40 to 5 Torr). The nanoparticle may notsubstantially sequester nitric oxide. The nanoparticle may limit theoxidation of oxygen-carrying agent to about 10% or less of the totalconcentration of oxygen-carrying agent in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising an oxygen carryingagent, an allosteric effector and a reducing agent. The payload is inthe interior of the nanoparticle. The amphiphilic polymer comprises abranched amine-containing polymer with reactive groups and is linked toa lipid via the reactive groups, such that at least about 55% of thefree reactive groups are linked to lipids. The surface reactive groupsof the amphiphilic polymer comprising the shell are cross-linked with abifunctional linker. The average diameter of the nanoparticle may befrom about 130 nm to about 300 nm, and the average height of thenanoparticle is from about 30 nm to about 80 nm. The nanoparticle maycomprise a through-hole or a depression. The branched polymer may be apolyethyleneimine branched polymer, a PAMAM dendrimer, a star polymer,or a graft polymer. The lipid may be palmitic acid orC24-pentacosadiynoic acid. The nanoparticle may comprise about 20 toabout 60% (w/v) oxygen-carrying agent molecules. The ratio ofoxygen-carrying agent to allosteric effector and oxygen-carrying agentto reducing agent may be about independently selected from the groupconsisting of 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1,3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, and 10:1. The nanoparticle designallows the effective release of O₂ during perfusion across the O₂tensions/gradients encountered in normal/abnormal human physiology (e.g.tissue pO₂ range from 40 to 5 Torr). The nanoparticle may notsubstantially sequester nitric oxide. The nanoparticle may limit theoxidation of oxygen-carrying agent to about 10% or less of the totalconcentration of oxygen-carrying agent in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising hemoglobin, 2,3-DPGand a reducing agent selected from the group consisting ofleucomethylene blue, ascorbate and glutathione. The payload is in theinterior of the nanoparticle. The amphiphilic polymer comprises abranched amine-containing polymer with reactive groups and is linked toa lipid via the reactive groups, such that at least about 25% of thefree reactive groups are linked to lipids. The surface reactive groupsof the amphiphilic polymer comprising the shell are cross-linked with abifunctional linker. The average diameter of the nanoparticle may befrom about 130 nm to about 300 nm, and the average height of thenanoparticle is from about 30 nm to about 80 nm. The nanoparticle maycomprise a through-hole or a depression. The branched polymer may be apolyethyleneimine branched polymer, a PAMAM dendrimer, a star polymer,or a graft polymer. The lipid may be palmitic acid orC24-pentacosadiynoic acid. The nanoparticle may comprise about 20 toabout 60% (w/v) hemoglobin molecules. The ratio of hemoglobin toallosteric effector and hemoglobin to reducing agent may be aboutindependently selected from the group consisting of 1:10, 1:9, 1:8, 1:7,1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1,and 10:1. The nanoparticle design allows the effective release of O₂during perfusion across the O₂ tensions/gradients encountered innormal/abnormal human physiology (e.g. tissue pO₂ range from 40 to 5Torr). The nanoparticle may not substantially sequester nitric oxide.The nanoparticle may limit the oxidation of hemoglobin to about 10% orless of the total concentration of hemoglobin in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising hemoglobin, 2,3-DPGand a reducing agent selected from the group consisting ofleucomethylene blue, ascorbate and glutathione. The payload is in theinterior of the nanoparticle. The amphiphilic polymer comprises abranched amine-containing polymer with reactive groups and is linked toa lipid via the reactive groups, such that at least about free 40% ofthe reactive groups are linked to lipids. The surface reactive groups ofthe amphiphilic polymer comprising the shell are cross-linked with abifunctional linker. The average diameter of the nanoparticle may befrom about 130 nm to about 300 nm, and the average height of thenanoparticle is from about 30 nm to about 80 nm. The nanoparticle maycomprise a through-hole or a depression. The branched polymer may be apolyethyleneimine branched polymer, a PAMAM dendrimer, a star polymer,or a graft polymer. The lipid may be palmitic acid orC24-pentacosadiynoic acid. The nanoparticle may comprise about 20 toabout 60% (w/v) hemoglobin molecules. The ratio of hemoglobin toallosteric effector and hemoglobin to reducing agent may be aboutindependently selected from the group consisting of 1:10, 1:9, 1:8, 1:7,1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1,and 10:1. The nanoparticle design allows the effective release of O₂during perfusion across the O₂ tensions/gradients encountered innormal/abnormal human physiology (e.g. tissue pO₂ range from 40 to 5Torr). The nanoparticle may not substantially sequester nitric oxide.The nanoparticle may limit the oxidation of hemoglobin to about 10% orless of the total concentration of hemoglobin in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising hemoglobin, 2,3-DPGand a reducing agent selected from the group consisting ofleucomethylene blue, ascorbate and glutathione. The payload is in theinterior of the nanoparticle. The amphiphilic polymer comprises abranched amine-containing polymer with reactive groups and is linked toa lipid via the reactive groups, such that at least about 55% of thefree reactive groups are linked to lipids. The surface reactive groupsof the amphiphilic polymer comprising the shell are cross-linked with abifunctional linker. The average diameter of the nanoparticle may befrom about 130 nm to about 300 nm, and the average height of thenanoparticle is from about 30 nm to about 80 nm. The nanoparticle maycomprise a through-hole or a depression. The branched polymer may be apolyethyleneimine branched polymer, a PAMAM dendrimer, a star polymer,or a graft polymer. The lipid may be palmitic acid orC24-pentacosadiynoic acid. The nanoparticle may comprise about 20 toabout 60% (w/v) hemoglobin molecules. The ratio of hemoglobin toallosteric effector and hemoglobin to reducing agent may be aboutindependently selected from the group consisting of 1:10, 1:9, 1:8, 1:7,1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1,and 10:1. The nanoparticle design allows the effective release of O₂during perfusion across the O₂ tensions/gradients encountered innormal/abnormal human physiology (e.g. tissue pO₂ range from 40 to 5Torr). The nanoparticle may not substantially sequester nitric oxide.The nanoparticle may limit the oxidation of hemoglobin to about 10% orless of the total concentration of hemoglobin in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising hemoglobin, 2,3-DPGand a reducing agent selected from the group consisting ofleucomethylene blue, ascorbate and glutathione. The payload is in theinterior of the nanoparticle. The amphiphilic polymer comprises PEI andis linked to a lipid via the reactive groups, such that at least about40% of the free primary amines are linked to lipids. The surfacereactive groups of the amphiphilic polymer comprising the shell arecross-linked with a bifunctional linker. The average diameter of thenanoparticle may be from about 130 nm to about 300 nm, and the averageheight of the nanoparticle is from about 30 nm to about 80 nm. Thenanoparticle may comprise a through-hole or a depression. The PEI mayhave a MW of 10 kDa to about 100 kDa or more. The lipid may be palmiticacid or C24-pentacosadiynoic acid. The nanoparticle may comprise about20 to about 60% (w/v) hemoglobin molecules. The ratio of hemoglobin toallosteric effector and hemoglobin to reducing agent may be aboutindependently selected from the group consisting of 1:10, 1:9, 1:8, 1:7,1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1,and 10:1. The nanoparticle design allows the effective release of O₂during perfusion across the O₂ tensions/gradients encountered innormal/abnormal human physiology (e.g. tissue pO₂ range from 40 to 5Torr). The nanoparticle may not substantially sequester nitric oxide.The nanoparticle may limit the oxidation of hemoglobin to about 10% orless of the total concentration of hemoglobin in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising hemoglobin, 2,3-DPGand a reducing agent selected from the group consisting ofleucomethylene blue, ascorbate and glutathione. The payload is in theinterior of the nanoparticle. The amphiphilic polymer comprises PEI andis linked to a lipid via the reactive groups, such that at least about50% of the free primary amines are linked to lipids. The surfacereactive groups of the amphiphilic polymer comprising the shell arecross-linked with a bifunctional linker. The average diameter of thenanoparticle may be from about 130 nm to about 300 nm, and the averageheight of the nanoparticle is from about 30 nm to about 80 nm. Thenanoparticle may comprise a through-hole or a depression. The PEI mayhave a MW of 10 kDa to about 100 kDa or more. The lipid may be palmiticacid or C24-pentacosadiynoic acid. The nanoparticle may comprise about20 to about 60% (w/v) hemoglobin molecules. The ratio of hemoglobin toallosteric effector and hemoglobin to reducing agent may be aboutindependently selected from the group consisting of 1:10, 1:9, 1:8, 1:7,1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1,and 10:1. The nanoparticle design allows the effective release of O₂during perfusion across the O₂ tensions/gradients encountered innormal/abnormal human physiology (e.g. tissue pO₂ range from 40 to 5Torr). The nanoparticle may not substantially sequester nitric oxide.The nanoparticle may limit the oxidation of hemoglobin to about 10% orless of the total concentration of hemoglobin in the nanoparticle.

In some embodiments, a nanoparticle has a substantially bi-concaved discshape, comprises an aqueous core and a bi-layered shell comprising anamphiphilic polymer, and has a payload comprising hemoglobin, 2,3-DPGand a reducing agent selected from the group consisting ofleucomethylene blue, ascorbate and glutathione. The payload is in theinterior of the nanoparticle. The amphiphilic polymer comprises PEI andis linked to a lipid via the reactive groups, such that at least about55% of the free primary amines are linked to lipids. The surfacereactive groups of the amphiphilic polymer comprising the shell arecross-linked with a bifunctional linker. The average diameter of thenanoparticle may be from about 130 nm to about 300 nm, and the averageheight of the nanoparticle is from about 30 nm to about 80 nm. Thenanoparticle may comprise a through-hole or a depression. The PEI mayhave a MW of 10 kDa to about 100 kDa or more. The lipid may be palmiticacid or C24-pentacosadiynoic acid. The nanoparticle may comprise about20 to about 60% (w/v) hemoglobin molecules. The ratio of hemoglobin toallosteric effector and hemoglobin to reducing agent may be aboutindependently selected from the group consisting of 1:10, 1:9, 1:8, 1:7,1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1,and 10:1. The nanoparticle design allows the effective release of O₂during perfusion across the O₂ tensions/gradients encountered innormal/abnormal human physiology (e.g. tissue pO₂ range from 40 to 5Torr). The nanoparticle may not substantially sequester nitric oxide.The nanoparticle may limit the oxidation of hemoglobin to about 10% orless of the total concentration of hemoglobin in the nanoparticle.

II. Process of Preparing Oxygen-Carrying Nanoparticles

Another aspect of the present disclosure is a process for thepreparation of a population of self-assembled, substantially bi-concaveddisk shaped nanoparticles. Generally speaking, a process comprisesforming an amphiphilic polymer; forming in a non-polar solvent aplurality of inverted micelles comprising the amphiphilic polymer;suspending a payload comprising an oxygen-carrying agent, an allostericeffector, and a reducing agent in a polar solvent and transferring thepayload into the organic layer comprising the inverted micelles byagitation; and self-assembly of the inverted micelles into substantiallybi-concaved disk shaped nanoparticles. The nanoparticle may bepegylated. Alternatively, the nanoparticle may be cross-linked. In stillanother alternative, the nanoparticle may be pegylated and cross-linked.

(a) Forming an Amphiphilic Polymer

A process for the preparation of a particle of the disclosure comprises,in part, forming an amphiphilic polymer. Generally speaking, a processcomprises hydrophobically modifying a branched polymer by covalentlyconjugating an amphiphilic lipid to the branched polymer. Suitablebranched polymers and amphiphilic lipids are detailed in Section Iabove. As described above, branched polymers comprise free reactivegroups. Free reactive groups may be amine groups.

Generally speaking, at least 25% of free reactive groups of the polymerare linked with amphiphilic lipid. For instance, about 25% to about 55%of free reactive groups of a polymer are linked with lipid, about 30% toabout 55% of free reactive groups of a polymer are linked with lipid,about 35% to about 55% of free reactive groups of a polymer are linkedwith lipid, about 40% to about 55% of free reactive groups of a polymerare linked with lipid, about 45% to about 60% of free reactive groups ofa polymer are linked with lipid, about 50% to about 65% of free reactivegroups of a polymer are linked with lipid, about 55% to about 70% offree reactive groups of a polymer are linked with lipid, about 60% toabout 75% of free reactive groups of a polymer are linked with lipid,about 65% to about 80% of free reactive groups of a polymer are linkedwith lipid, about 70% to about 85% of free reactive groups of a polymerare linked with lipid, about 75% to about 90% of free reactive groups ofa polymer are linked with lipid, about 80% to about 95% of free reactivegroups of a polymer are linked with lipid, about 85% to about 100% offree reactive groups of a polymer are linked with lipid. Alternatively,about 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%,38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%,52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 66%,67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%,81%, 82%, 83%, 84%, 85%, 86%, ⁸⁷%^(,) 88%, 89%, 90%, 91%, 92%, 93%, 94%,95%, 96%, 97%, 97%, 98%, 99 or more of free reactive groups of a polymerare linked with lipid. The molar ratio of polymer to lipid is typicallyfrom about 1:0.4 to about 1:0.8. In general, molar ratio of polymer tolipid may be about 1:0.4, 1:0.45, 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7,1:0.75, or 1:0.8.

Methods of covalently conjugating a lipid to a polymer are known in theart and detailed in the examples. Briefly, an active group of a polymerforms a covalent bond with an active group of a lipid. Suitable polymeractive groups are detailed above. A lipid may comprise a suitable activegroup for forming a bond with a polymer active group (i.e., directconjugation), or may be treated with a linker to provide a suitableactive group (i.e., indirect conjugation). Non-limiting examples ofactive groups may include epoxides, carboxylates, oxiranes, esters ofN-hydroxysuccinimide, aldehydes, hydrazines, maleimides, mercaptans,amino groups, alkylhalides, isothiocyanates, carbodiimides, diazocompounds, tresyl chloride, tosyl chloride, propargyl, azide, andtrichloro S-triazine. In general, reactive groups may be photoreactivegroups, that when contacted with light may become activated, and capableof covalently attaching to the polymer reactive groups. Exemplaryphoto-reactive groups may include aryl azides, diazarenes,beta-carbonyldiazo, and benzophenones. Reactive species are nitrenes,carbenes, and radicals. These reactive species are generally capable ofcovalent bond formation. Preferably, reactive groups are carboxyl andamine.

(b) Forming a Plurality of Inverted Micelles

A process for the preparation of a nanoparticle further comprises, inpart, forming a plurality of inverted micelles. Generally speaking,unimolecular inverted micelles (i.e., reversed micelles) are formed byagitating a mixture of an amphiphilic polymer from Section II(a) abovewith a non-polar solvent. Typically, the concentration of amphiphilicpolymer in a non-polar solvent is about 10⁻⁷ to about 10⁻⁵ M. Ingeneral, the concentration of amphiphilic polymer is about 10⁻⁶ M.

The non-polar solvent may be organic. Non-limiting examples of non-polarsolvents may include acetone, methyl acetate, ethyl acetate, hexane,benzene, toluene, diethyl ether, dichloromethane, and chloroform. Anexemplary solvent may be chloroform or dichloromethane.

A mixture may be agitated through physical inversion, vortexing, mixing,shaking, sonicating, stirring, or other similar means. Typically, amixture may be agitated for about 1 minute to about 10 minutes, althoughlonger agitation times may be possible. A mixture may be agitated forabout 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 minutes or more. Generally speaking,the agitation is performed at about 4° C. to about room temperature.

(c) Transfer of the Payload Into the Organic Layer Comprising theInverted Micelles

A nanoparticle comprises a payload, the payload comprising anoxygen-carrying agent, an allosteric effector, and a reducing agent. Anoxygen-carrying agent, an allosteric effector, and a reducing agent maybe as described in Section I(f) above. A payload is mixed with anaqueous solvent and the mixture is added to the non-polar solventmixture of the inverted micelles resulting in a bi-phasic mixture. Thebi-phasic mixture is allowed to settle down, if needed, and then thepayload is transferred to the organic layer comprising the invertedmicelles by agitation. Typically, only minimal agitation is required,and physical inversion and/or swirling or shaking is sufficient totransfer an oxygen-carrying agent, an allosteric effector, and areducing agent to the interior of the inverse micelles. Agitation mayalso be by high shear mixing. Non-limiting examples of high-shear mixingmay include microfluidization, sonication, homogenization, or relatedmixing. An aqueous solvent may be the polar solvent described in SectionII(d).

(d) Self-Assembly of a Bi-Concaved Disc Shaped Nanoparticle

After formation of a plurality of inverted micelles comprising thepayload in Section II(c) above, a process of the disclosure comprisesself-assembly of inverted micelles into a substantially bi-concaved discshaped nanoparticle. Generally speaking, a process comprises agitatinginverted micelles in the presence of heat and a solvent system.

The temperature during the agitating dictates, in part, the size ofresulting nanoparticles. Typically, as the temperature increases, thesize of nanoparticles increases. The temperature during the agitationmay range from about 30° C. to about 65° C. For instance, thetemperature may be about 30, 35, 40, 45, 50, 55, 60, or 65° C.

A mixture may be agitated via physical or acoustical means. Forinstance, a mixture may be agitated by physical inversion, vortexing,mixing, shaking, sonicating, or other similar means. Preferably, amixture may be agitated by high shear mixing. Generally, the invertedmicelles are agitated for about 15 min to about 90 min, for about 30 minto about 60 min, or for about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or70 min.

Inverted micelles are typically agitated, with heat, in the presence ofa solvent system. A solvent system comprises both a polar solvent and anon-polar solvent. For instance, a polar solvent is an aqueous solventand a non-polar solvent is an organic solvent. By way of example, anon-polar solvent may be the non-polar solvent used in Section II(b)above, and an aqueous solvent may be added, with brief agitation, to thenon-polar solvent. To achieve an appropriate ratio between a polar andnon-polar solvent, a non-polar solvent may be evaporated from themixture. The weight ratio of a polar and non-polar solvent may be about1:5. An exemplary polar solvent may be methanol and an exemplarynon-polar solvent may be chloroform.

To achieve an appropriate ratio between a polar and non-polar solvent,the non-polar solvent may be evaporated from the mixture. Theevaporation may be performed under reduced pressure. Generally speaking,the pressure selected will depend, in part, on the non-polar solvent.The reduced pressure may be between about 350 mbar and 1000 mbar, orabout 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, or 950mbar. When a non-polar solvent is chloroform, the reduced pressure maybe between about 400 and about 500 mbar. For instance, the reducedpressure may be between about 400 mbar and about 450 mbar, or betweenabout 420 mbar and about 440 mbar.

(e) Optional Molecules

A nanoparticle may further comprise at least one molecule selected fromthe group consisting of a targeting moiety, a biologically active agent,a contrast agent, a metal atom, and a therapeutic agent. Suitablemolecules are detailed above. These molecules may be conjugated to thesurface of the shell of a nanoparticle or contained in the interior ofthe nanoparticle.

Molecules may be incorporated into the shell of a nanoparticle. Toincorporate such a molecule, a targeting moiety, biologically activeagent, imaging agent, metal atom, or therapeutic agent is typicallyadded to a mixture comprising a plurality of inverted micelles in anon-polar solvent described in Section II(b) above. After mixing, amolecule is incorporated into micelles by phase transition from aqueousto organic phase. As a result, after self-assembly, a molecule isincorporated into the shell of the nanoparticle.

A water soluble biologically active agent, imaging agent, metal atom, ortherapeutic agent may be incorporated into the aqueous core of ananoparticle. To incorporate such a molecule, a biologically activeagent, imaging agent, metal atom, or therapeutic agent may betransferred to the interior of an inverted micelle. For instance, afterformation of a plurality of micelles, but before the self-assembly ofnanoparticles, the plurality of micelles may be mixed with the watersoluble molecule. The mixture may be agitated, and as a result, a watersoluble molecule is transferred to the interior of inverted micelles,and consequently, to the aqueous core of a nanoparticle after theself-assembly of the inverted micelles. Typically, only minimalagitation is required, and physical inversion is sufficient to transfera water soluble molecules to the interior of inverse micelles.

A water insoluble targeting moiety, metal atom, biologically activeagent, imaging agent, or therapeutic agent may also be located within ahydrophobic region of an amphiphilic polymer comprising the shell of ananoparticle. To incorporate such a molecule, a water insoluble moleculemay be dissolved in organic non polar solvent and mixed with theinverted micelles. Consequently, a water insoluble molecule istransferred to the hydrophobic region of the amphiphilic polymer afterthe self-assembly of inverted micelles.

A targeting moiety, biologically active agent, imaging agent, metalatom, or therapeutic agent may be located within the hydrophilic regionof the amphiphilic polymer or the surface of the outer of ananoparticle. A molecule may be adsorbed to the surface throughnon-covalent bonds, or covalently bonded to the amphiphilic polymer. Forinstance, a molecule may be bonded to the surface of the nanoparticlethrough covalent bonding, dative bonding, ionic bonding, hydrogenbonding or Van der Waals bonding.

(f) Cross-Linking

After the self-assembly of a nanoparticle, the shell may becross-linked. As detailed above, cross-linking may be used to alter therate of release of oxygen and therapeutic molecules. Alternatively,cross-linking may be used to increase the stability of a nanoparticle.The particles may be cross-linked on the surface of the outer shell, ormay be cross-linked within the outer shell. The cross-linking may bechemical cross-linking or photochemical cross-linking. Methods ofcross-linking are known in the art. Briefly, suitable cross-linkers willreact with one or more active groups of the amphiphilic polymer.Cross-linkers may be homobifunctional or heterobifunctional.Cross-linkers may be chemical cross-linkers or non-chemicalcross-linkers. Suitable chemical cross-linkers may includeglutaraldehyde, bis-carboxylic acid spacers, or bis-carboxylicacid-active esters. Photochemical cross-linking may be achieved byuv-crosslinking of polydiacetylinic bonds. One of ordinary skill in theart would recognize that a suitable cross-linker can and will varydepending on a composition of a nanoparticle and the intended use.

(g) Pegylation

A particle of the disclosure may be pegylated. As used herein,“pegylation” refers to the addition of polyethylene glycol to the outershell. Methods of pegylation are commonly known in the art and detailedin the examples. The pegylation may be used to decrease the zeta surfacecharge of the nanoparticle. Stated another way, pegylation may be usedto impart a near neutral surface of a nanoparticle. The pegylation maybe used to alter the in vivo circulation of a nanoparticle.

(h) Sterilization and Lyophilization

Sterility of nanoparticle compositions are important for in vivoapplications. Sterilization may be accomplished through any method knownin the art, provided the method does not materially affect particlestability and/or O₂ binding/release. For example, nanoparticlescompositions or solutions may be filtered sterilized through membraneswith a pore size of 0.22 μm or less. Non-limiting examples of suitablemembranes include hydrophobic polytetrafluoroethylene, hydrophilicDurapore®(polyvinylidene fluoride) and polyethersulfone. Filtrationefficiency may be determined for each membrane by comparing applied andrecovered volumes, particle size, and/or zeta potential.

Nanoparticle aliquots in buffered suspension may be dried to a powderand sealed under an inert gas as the lyophilized powder with or withouta cryoprotectant. Preferably, suspensions of aliquots are lyophilized,though other methods known in the art may be used. Suitable inert gasesare known in the art and may include, but are not limited to, argon.Similarly, suitable cyroprotectants are known in the art and mayinclude, but are not limited to sorbitol. Reconstituted aliquots may beevaluated for altered particle size, zeta potential, pH, viscosity,sterility, and/or O₂ dissociation as described herein. Accepted storageconditions, expiration dating, and release specifications will reflectless than 20%, more preferably less than 15%, even more preferably lessthan 10% change from baseline properties. The lyophilized powder may bereconstituted in a fashion that is tailored for the intended use, and/orthe status of patients' circulating blood volume. For example, a bloodsubstitute composition comprising a nanoparticle of the disclosure maybe composed in a more concentrated fashion to be administered tonormovolemic patients with anemia or in a more dilute fashion to beadministered to hypovolemic patients with hemorrhage.

III. Blood Substitute Compositions Comprising Nanoparticles

A further aspect of the disclosure encompasses blood substitutecompositions comprising nanoparticles of the disclosure. Typically,nanoparticles are formulated as a composition for use as a bloodsubstitute for in vivo, in vitro, in situ, or ex vivo use.

Blood substitute nanoparticles may be formulated by mixing nanoparticleswith optional excipients and a suitable diluent. The concentration ofnanoparticles in the diluent may vary according to the application.Preferably, the concentration of nanoparticles may be about4×10¹²−6×10¹² nanoparticles/ml.

A composition comprising a plurality of nanoparticles may be a drypowder such as a lyophilized composition comprising nanoparticles.Alternatively, a composition comprising a plurality of nanoparticles maybe a solution, a mixture, or a suspension. A non-limiting example of asuspension is a colloid. Generally speaking a colloid is a suspension offine particles that do not readily settle out of the suspension. A drypowder may be formed of nanoparticles in accordance with knowntechniques such as freeze drying or lyophilization. A dry powdercomprising nanoparticles may then be reconstituted by mixing with anaqueous solution to produce a liquid blood substitute.

The composition may be formulated and administered to a subject byseveral different means that will supplement the oxygen-carryingcapacity of a subject's blood. Such compositions may generally beadministered intravascularly in dosage unit formulations containingconventional nontoxic pharmaceutically acceptable carriers, adjuvants,excipients, and vehicles as desired.

Injectable preparations, for example, sterile injectable aqueous oroleaginous suspensions, may be formulated according to the known artusing suitable dispersing or wetting agents and suspending agents. Thesterile injectable preparation may also be a sterile injectable solutionor suspension in a nontoxic parenterally acceptable diluent or solvent.Among the acceptable vehicles and solvents that may be employed arewater, Ringer's solution, Lactate Ringer's solutions, and isotonicsodium chloride solution. In addition, sterile, fixed oils areconventionally employed as a solvent or suspending medium. For thispurpose, any bland fixed oil may be employed, including synthetic mono-or diglycerides. In addition, fatty acids such as oleic acid are usefulin the preparation of injectables. Dimethyl acetamide, surfactantsincluding ionic and non-ionic detergents, and polyethylene glycols canbe used. Mixtures of solvents and wetting agents such as those discussedabove are also useful.

IV. Methods of Using Oxygen-Carrying Nanoparticles

Another aspect of the disclosure encompasses methods of using thebi-concaved shaped oxygen-carrying nanoparticles of the disclosure. Inessence, an oxygen-carrying nanoparticles are capable of deliveringoxygen. As such, oxygen-carrying nanoparticles may be used to deliveroxygen to a subject in need of a rapid restoration of O₂ levels or anincreased O₂ level, or a replacement of O₂ levels is clinicallyindicated. Oxygen-carrying nanoparticles may be used to supplement theoxygen-carrying capacity of a subject's blood, to treat a subject inneed of blood, or to conduct blood transfusion in a patient. Typically,nanoparticles are formulated as a composition for in vivo, in vitro, insitu, or ex vivo use as described in Section III above.

A composition of nanoparticles may be administered to a subject todeliver oxygen to a biological tissue. Suitable subjects include, butare not limited to, mammals, amphibians, reptiles, birds, and fish.Suitable mammals include, but are not limited to, humans, horses, catsand dogs.

Biological tissue, as used herein, may refer to cells, organs, tumors,or material associated with cells, organs, or tumors, such as bloodclots. Suitable tissues may include, but are not limited to, heart,lungs, brain, eye, stomach, spleen, bones, pancreas, gall bladder,kidneys, liver, intestines, skin, uterus, bladder, eyes, lymph nodes,blood vessels, and blood and lymph components.

The numerous settings in which oxygen delivery using oxygen-carryingnanoparticles of the disclosure find use include the following:

Trauma. An acute loss of whole blood can result in a fluid shift fromthe interstitial and intracellular spaces to replace the lost volume ofblood while shunting of blood away from the low priority organsincluding the skin and gut. Shunting of blood away from organs reducesand sometimes eliminates O₂ levels in these organs and results inprogressive tissue death.

Ischemia. In ischemia, a particular organ (or organs) are “starved” foroxygen. Small sections of the organ, known as infarcts, begin to die asa result of the lack of O₂. Rapid restoration of O₂ levels is criticalis stemming infarct formation in critical tissues. Conditions resultingin ischemia include heart attack, stroke, or cerebrovascular trauma.

Hemodilution: In this clinical application, a blood substitute isrequired to replace blood that is removed pre-operatively. It iscontemplated that patient blood removal occurs to prevent a requirementfor allogeneic transfusions post-operatively. In this application, theblood substitute is administered to replace (or substitute for) the O₂levels of the removed autologous blood. This permits the use of theremoved autologous blood for necessary transfusions during and aftersurgery. One such surgery requiring pre-operative blood removal would bea cardiopulmonary bypass procedure.

Septic Shock. In overwhelming sepsis, some patients may becomehypertensive in spite of massive fluid therapy and treatment withvasocontrictor agents. In this instance, the overproduction of nitricoxide (NO) results in the lowered blood pressure. Therefore hemoglobinis close to an ideal agent for treatment of these patients becausehemoglobin binds NO with an avidity that parallels O₂.

Cancer. Delivery of O₂ to the hypoxic inner core of a tumor massincreases its sensitivity to radiotherapy and chemotherapy. Because themicrovasculature of a tumor is unlike that of other tissues,sensitization through increasing O₂ levels requires O₂ be unloadedwithin the hypoxic core. In other words, the p50 should be very low toprevent early unloading of the O₂, increasing the O₂ levels, to insureoptimal sensitization of the tumor to subsequent radiation andchemotherapy treatments.

Chronic anemia. In these patients, replacement of lost or metabolizedhemoglobin is compromised or completely absent. It is contemplated thatthe blood substitute must effectively replace or increase the reduced O₂levels in the patient.

Sickle cell anemia. In sickle cell anemia, the patient is debilitated bya loss of O₂ levels that occurs during the sickling process as well as avery high red blood cell turnover rate. The sickling process is afunction of pO₂ where the lower the pO₂, the greater the sickling rate.It is contemplated that the ideal blood substitute would restore patientO₂ levels to within a normal range during a sickling crisis.

Cardioplegia. In certain cardiac surgical procedures, the heart isstopped by appropriate electrocyte solutions and reducing patienttemperature. Reduction of the temperature will significantly reduce thep50, possibly preventing unloading of O₂ under any ordinaryphysiological conditions. Replacement of O₂ levels is contemplated aspotentially reducing tissue damage and death during such procedures.

Hypoxia. Soldiers, altitude dwellers, and world-class athletes underextreme conditions may suffer reduced O₂ levels because extraction of O₂from air in the lung is limited. The limited O₂ extraction furtherlimits O₂ transport. It is contemplated that a blood substitute couldreplace or increase the O₂ levels in such individuals.

Organ Perfusion. During the time an organ is maintained ex vivo,maintaining O₂ content is essential to preserving structural andcellular integrity and minimizing infarct formation. It is contemplatedthat a blood substitute would sustain the O₂ requirements for such anorgan.

Cell Culture. This requirement is virtually identical to that of organperfusion, except that the rate of O₂ consumption may be higher.

Hematopoiesis. It is contemplated that the blood substitute serves as asource for heme and iron for use in the synthesis of new hemoglobinduring hematopoiesis.

The present disclosure may also be used in non-humans. The methods andcompositions of the present disclosure may be used with domestic animalssuch as livestock and companion animals (e.g., dogs, cats, horses,birds, reptiles), as well as other animals in aquaria, zoos, oceanaria,and other facilities that house animals. It is contemplated that thepresent disclosure finds utility in the emergency treatment of domesticand wild animals suffering a loss of blood due to injury, hemolyticanemias, etc. For example, it is contemplated that embodiments of thepresent disclosure are useful in conditions such as equine infectiousanemia, feline infectious anemia, hemolytic anemia due to chemicals andother physical agents, bacterial infection, Factor IV fragmentation,hypersplenation and splenomegaly, hemorrhagic syndrome in poultry,hypoplastic anemia, aplastic anemia, idiopathic immune hemolyticconditions, iron deficiency, isoimmune hemolytic anemia,microangiopathic hemolytic, parasitism, etc. In particular, the presentdisclosure finds use in areas where blood donors for animals of rareand/or exotic species are difficult to find.

DEFINITIONS

As used herein, the term “allosteric effector” refers to a molecule thatmodulates the rate or amount of oxygen binding to or releasing from ofan oxygen carrier.

The phrase “exterior of a nanoparticle”, as used herein, refers to theouter layer of the nanoparticle shell and any component(s) attachedcovalently or non-covalently to the outer layer of the nanoparticleshell, or any component(s) within the outer layer of the nanoparticleshell. For example, the exterior of a nanoparticle may also comprise anoptional molecule.

The term “hemoglobin” is used herein to generally refer to a proteinthat may be contained within a red blood cell that transports oxygen.Each molecule of hemoglobin has 4 subunits, 2 a chains and 213 chains,which are arranged in a tetrameric structure. Each subunit also containsone heme group, which is the iron-containing center that binds oxygen.Thus, each hemoglobin molecule can bind 4 oxygen molecules. “Hemoglobin”refers to naturally occurring or synthetic hemoglobin. Hemoglobin may beisolated and purified from a human or animals, or may be produced bychemical synthesis and recombinant techniques.

The term “hemoglobin free of stroma”, as used herein, refers tohemoglobin from which all red blood cell membranes have been removed.

The term “hemodynamic parameters”, as used herein, refers broadly tomeasurements indicative of blood pressure, flow and volume status,including measurements such as blood pressure, cardiac output, rightatrial pressure, and left ventricular end diastolic pressure.

The phrase “interior of a nanoparticle”, as used herein, refers to theany portion of the nanoparticle that is not the exterior of thenanoparticle. The interior of a nanoparticle comprises the inner layerof the nanoparticle shell, the hydrophobic region between the inner andouter layer of the nanoparticle shell, the aqueous core and the payload.The interior of a nanoparticle may also comprise an optional molecule.

The term “methemoglobin”, as used herein, refers to an oxidized form ofhemoglobin that contains iron in the ferric state and cannot function asan oxygen carrier.

The term “perfluorocarbons”, as used herein, refers to synthetic, inert,molecules that contain fluorine atoms, and that consist entirely ofhalogen (Br, F, Cl) and carbon atoms. In the form of emulsions, they areunder development as blood substances, because they have the ability todissolve many times more oxygen than equivalent amounts of plasma orwater.

The term “modified hemoglobin” includes, but is not limited to,hemoglobin altered by a chemical reaction such as intra- andinter-molecular cross-linking, genetic manipulation, polymerization,and/or conjugation to other chemical groups (e.g., polyalkylene oxides,for example polyethylene glycol, or other adducts such as proteins,peptides, carbohydrates, synthetic polymers and the like). In essence,hemoglobin is “modified” if any of its structural or functionalproperties have been altered from its native state. As used herein, theterm “hemoglobin” by itself refers both to native, unmodified,hemoglobin, as well as modified hemoglobin.

The terms “nanoparticle” and “oxygen-carrying nanoparticle” usedinterchangeably throughout the application.

The term “oxygen affinity” refers to the avidity with which an oxygencarrier such as hemoglobin binds molecular oxygen. This characteristicis defined by the oxygen equilibrium curve which relates the degree ofsaturation of hemoglobin molecules with oxygen (Y axis) with the partialpressure of oxygen (X axis). The position of this curve is denoted bythe value, p50, the partial pressure of oxygen at which the oxygencarrier is half-saturated with oxygen, and is inversely related tooxygen affinity. Hence the lower the p50, the higher the oxygenaffinity. The oxygen affinity of whole blood (and components of wholeblood such as red blood cells and hemoglobin) can be measured by avariety of methods known in the art. (See, e.g., Winslow et al., J.Biol. Chem. 252(7):2331-37 (1977)). Oxygen affinity may also bedetermined using a commercially available HEMOX™ Analyzer (TCSScientific Corporation, New Hope, Pa.). (See, e.g., Vandegriff andShrager in “Methods in Enzymology” (Everse et al., eds.) 232:460(1994)).

The term “oxygen-carrying capacity,” or simply “oxygen capacity” refersto the capacity of a blood substitute to carry oxygen, but does notnecessarily correlate with the efficiency in which it delivers oxygen.Oxygen-carrying capacity is generally calculated from hemoglobinconcentration, since it is known that each gram of hemoglobin binds 1.34ml of oxygen. Thus, the hemoglobin concentration in g/dl multiplied bythe factor 1.34 yields the oxygen capacity in ml/dl. Hemoglobinconcentration can be measured by any known method, such as by using theβ-Hemoglobin Photometer (HemoCue, Inc., Angelholm, Sweden). Similarly,oxygen capacity can be measured by the amount of oxygen released from asample of hemoglobin or blood by using, for example, a fuel cellinstrument (e.g., Lex-O2-Con; Lexington Instruments).

The term “oxygen-carrying component” refers broadly to a substancecapable of carrying oxygen in the body's circulatory system anddelivering at least a portion of that oxygen to the tissues. Theoxygen-carrying component may be native or modified hemoglobin, and mayalso be referred to herein as a “hemoglobin based oxygen carrier,” or“HBOC”.

The term “payload” refers to the components contained within theinterior of a nanoparticle. A payload comprises an oxygen-carryingagent, an effector agent, and a reducing agent. A payload may furthercomprise optional molecules.

The terms “shell” and “bi-layered shell” are used interchangeably, andgenerally refer to the shell of a nanoparticle. A shell is bi-layered,comprised of a hydrophilic outer layer, a hydrophilic inner layer, and ahydrophobic region between the layers.

Having described the disclosure in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the disclosure defined in the appended claims.

EXAMPLES

The following examples are included to demonstrate the disclosure. Itshould be appreciated by those of skill in the art that the techniquesdisclosed in the following examples represent techniques discovered bythe inventors to function well in the practice of the disclosure. Thoseof skill in the art should, however, in light of the present disclosure,appreciate that many changes could be made in the disclosure and stillobtain a like or similar result without departing from the spirit andscope of the disclosure, therefore all matter set forth is to beinterpreted as illustrative and not in a limiting sense.

Example 1 Preparation of Nanoparticles

Preparation and loading of biconcave nanoparticles is as described inPan et al., 2008 J Am Chem Soc 130:9186-9187, PCT Application No.PCT/US2008/079414, and US Publication No. 2010/0297007, all of which areincorporated herein in their entirety. A schematic representation of theparticles and preparation of the nanoparticles is shown in FIG. 1.

Polyethyleneimine polymers were grafted with hydrophobic alkyl groups bycovalent means. Palmitic acid was activated with the carbodiimide EDAC(1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, hydrochloride) followedby addition of the polymer to achieve greater than 50% functionalizationof free primary amine groups. The amphiphilic polymer assumes a 7-10 nmsized unimolecular inverted micellar structure in organic solvent aftervortexing.

Hemoglobin, hemoglobin and 2,3-DPG, or hemoglobin, 2,3-DPG, andleucomethylene blue or leucobenzyl methylene blue were loaded into thenanoparticles. Nanoparticles are loaded by adding solutions comprisinghemoglobin, hemoglobin and 2,3-DPG, or hemoglobin, 2,3-DPG, andleucomethylene blue or leucobenzyl methylene blue to an aqueoussuspension of nanoparticles, followed by briefly shaking/swirling.

Hemoglobin was human hemoglobin extracted and purified from expiredRBCs. Hemoglobin was stabilized as carboxyhemoglobin (HbCO), purifiedvia ion-exchange chromatography, and concentrated using ultrafiltrationto 4.0 g/dL. The concentration of hemoglobin used to generate thenanoparticles was 10 mg/mL. The concentration of 2,3-DPG was 10 mg/mL.The concentration of leucomethylene blue or leucobenzyl methylene bluewas 5 mg/mL. The nanoparticles comprised an average of 3488 hemoglobinmolecules per nanoparticle.

Nanoparticle sizes, shape, and morphology were measured by TEM, DLS, andAFM among other methods. Nanoparticles had a hydrodynamic diameter of150-180 nm, or 173±10 nm after re-suspension, with polydispersity of0.26±0.01, and zeta potential of ˜12±2 mV. Assays were performed asdescribed in Pan D, Caruthers S D, Hu G, Senpan A, Scott M J, Gaffney PJ, Wickline S A, Lanza G M. Ligand-directed nanobialys as theranosticagent for drug delivery and manganese-based magnetic resonance imagingof vascular targets. J Am Chem Soc. 2008; 130:9186-9187.

Following self-assembly, surface chemical cross-linking is achievedusing Sulfo-EGS (ethylene glycol bis[sulfosuccinimidylsuccinate], PBS,pH 8.5) in combination with hydroxylamine for 5 h at 37° C. Crosslinkinghas limited effect on particle size and zeta potential: 167±56 nm, +7±2mV, respectively.

Example 2 Oxygen Binding Characteristics of Labeled and UnlabeledNanoparticles

Nanoparticles produced labeled with leucobenzyl methylene blue orunlabeled nanoparticles were resuspended in water, and used forcharacterization of oxygen binding characteristics. Nanoparticles wereproduced generally as described in Example 1. The resulting solution hada total concentration of 5×10¹² nanoparticles/ml, and 2 g/l of glycatedhemoglobin.

A Hemox Analyzer was used to characterize oxygen binding-dissociation ofthe nanoparticles at pH10, 8, 6, and pH8.5. All measurements weregenerated at 37.3° C. In general, non-labeled particles exhibitedsignificantly higher p50 (lower affinity for oxygen) at low pH thanlabeled nanoparticles (FIG. 2 and Table 1).

At all pH measurements, p50 of nanoparticles are generally lower thanthe p50 of human blood, which is typically 26.6 mm Hg (53.2 mm Hg inthese readings). A generally lower p50 indicates a higher affinity foroxygen. A Bohr effect (right shift with decreased pH) was observed fornon-labeled nanoparticles, but not for labeled nanoparticles. Inaddition, oxygen binding-dissociation curves were measured using freshlyprepared nanoparticles, and particles that were in storage for about onemonth. In short, older hemoglobin generates oxygen binding-dissociationcurves with more noise in the recordings (FIG. 2).

TABLE 1 p50 mmHg pH With 2,3 DPG Without 2,3 DPG 6 20.85 23.36 47.2258.98 8 19.23 17.9 22.57 22.2 8.5 21.91 16.92 42.88 39.12 9 — — 20.4219.7 10 20.37 14.62 19.29 17.45 Note: The actual p50 values are half ofwhat's listed, due to the recording software set up.

Example 3 Characterization of Nanoparticles from Example 1

O₂ affinity and reversible binding was characterized using a blood-gasanalyzer. p50 (O₂ tension at HbSO₂=50%) was based on Hill's n (log[HbSO₂/(1-HbSO₂)]/log pO₂) and determined at 37° C. Under pO₂ of 720mmHg and pH of 7.3, HbSO₂ was 99.99% with [log [p0₂(7.4)]=2.807332496;1/k=3800.503808]; as such p50 was calculated to be 21.18 mmHg (in normalRBCs, p50 for HbA_(o), is 26.5 and for Hb_(F) is 20.0 mmHg).

NO scavenging and inappropriate vasoconstriction has been problematicfor HBOCs and appears to increase cardiovascular complications afterHBOC use. In a preliminary NO binding experiment, NO gas was bubbledthrough a nanoparticle suspension (RT, 15 min). UV-Vis absorbanceanalysis revealed no spectral peaks corresponding to the heme adducttypically observed following scavenging (Fe(II)NO, with peaks at 415,479, 542, 610 nm).

Rheological properties of an O₂ carrier are critically important sincethe anticipated volume administered alter blood viscosity andhemodynamics. The nanoparticles' influence upon plasma rheology wasstudied after suspension in NZW rabbit plasma, revealing that limitedeffect on plasma viscosity (FIG. 3A). The minor reduction in suspensionviscosity was related to the dilution of the plasma by the aqueous mediaof the nanoparticles. The absence of viscosity increase by thenanoparticle composition suggests that the nanoparticles do notaggregate in the presence of plasma proteins and will exert minimalinfluence on the rheological parameters of plasma.

Pharmacokinetic (pK) profile for the nanoparticles was determined inrats by incorporating radiolabeled Hb (^(99m)Tc tracer, dose 50 μCi/kg).Tracer activity was measured serially and adjusted for decay (FIG. 3B).PK parameters were determined by routine nonlinear compartmentalmodeling, as we have described185. Standard two compartment modelingresulted in good fit, with distribution t_(1/2)=26.2±3.6 min andelimination t_(1/2)=300±12 min (R²>0.96).

Example 4 Optimization of Nanoparticles for O₂ Binding/ReleaseCharacteristics

Nanoparticle synthesis may be optimized for O₂ delivery capacity andkinetics, as appropriate to relieve tissue hypoxia in the setting ofsevere anemia. As noted in Example 3, nanoparticles with a p50 of 21.18mmHg have been produced (p50 for HbAo (non-glycated hemoglobin) is 26.5;HbF (fetal hemoglobin) is 20.0 mmHg). Similarly, nanoparticles havingformulations with p50 of˜20 (high affinity, current formulation), 25(normal affinity), and 30 (low affinity) may be generated.

For example, Hb and amphiphilic polymer mixture (preloaded/not with2,3-DPG and LMB) will undergo self-assembly in phosphate buffer (PB) atpH 7.3. [Hb] in the buffer can be titrated to different concentrations,for example between 100, 150, 200, 250 and 300 mg/mL. Nanoparticlesurface chemical cross-linking can utilize Sulfo-EGS, in combinationwith hydroxylamine (PB buffer, pH 8.5, 5 h, 37° C.), followed bydialysis against 50 mM PB to remove the sulfo-EGS by-product. Particlesize, polydispersity, and zeta potential for each nanoparticleformulation can be evaluated, as described in Example 3.

Development can be informed by an analysis of O₂ affinity. O₂dissociation curves can be determined for each nanoparticle formulationas a function of temperature, pCO₂ and pH and can be referenced tovalues for fresh human red blood cells (RBCs) obtained from volunteers,after washing and resuspension in Krebs buffer, as described in Rogers SC, Said A, Corcuera D, McLaughlin D, Kell P, Doctor A. Hypoxia limitsantioxidant capacity in red blood cells by altering glycolytic pathwaydominance. O₂ dissociation and association hysteresis curves across thefull range of gas tensions encountered in human physiology can bemeasured using a HEMOX analyzer as described in Guarnone R, Centenara E,Barosi G. Performance characteristics of hemox-analyzer for assessmentof the hemoglobin dissociation curve. Haematologica. 1995; 80:426-430;p50 and cooperativity (Hill) coefficients can be calculated according tothe Adair equation as described in Kobayashi M, Ishigaki K, Kobayashi M,Imai K. Shape of the haemoglobin-oxygen equilibrium curve and oxygentransport efficiency. Respir Physiol. 1994; 95:321-328 or Kobayashi M,Satoh G, Ishigaki K. Sigmoid shape of the oxygen equilibrium curve andthe p50 of human hemoglobin. Experientia. 1994; 50:705-707. Nanoparticleand RBC suspensions can be matched by equimolar [Hb]. Absolute [Hb] andHb:2,3DPG molar ratios can be manipulated to create formulations withp50 (torr) of˜20 (high affinity), 25 (normal affinity), and 30 (lowaffinity) for efficacy testing. The efficacy of the 2,3-DPGshuttle/reservoir can be evaluated by determining the pH-dependent shiftin p50 and, if needed, PEI inner shell amine availability can be variedto maximize p50 shift between pH 7.2 (tissue) and 7.8 (lung).

Development of such nanoparticles may also be informed by measurement ofO₂ binding-release across the full range of physiologic gas tensions.The isolated-perfused murine lung (IPL) is ideally suited to evaluatenanoparticle O₂ loading & unloading kinetics during perfusion atphysiologically relevant rates in an intact vascular bed. The IPL can beprepared as described in Doctor A, Platt R, Sheram M L, Eischeid A,McMahon T, Maxey T, Doherty J, Axelrod M, Kline J, Gurka M, Gow A,Gaston B. Hemoglobin conformation couples erythrocyte s-nitrosothiolcontent to O₂ gradients. Proceedings of the National Academy ofSciences. 2005; 102:5709-5714; Maxey T S, Enelow R I, Gaston B, Kron IL, Laubach V E, Doctor A. Tumor necrosis factor-alpha from resident lungcells is a key initiating factor in pulmonary ischemia-reperfusioninjury. J. Thorac. Cardiovasc. Surg. 2004; 127:541-547; or Zhao M,Fernandez L G, Doctor A, Sharma A K, Zarbock A, Tribble C G, Kron I L,Laubach V E. Alveolar macrophage activation is a key initiation signalfor acute lung ischemia-reperfusion injury. AJP—Lung Cellular andMolecular Physiology. 2006; 291 :L1018-L1026. Nanoparticle formulationsor washed human RBCs suspensions (equimolar for Hb, 2 mM) can beperfused at pulmonary transit times of 2, 4, and 8 seconds, thencollected as left atrial efflux (without air exposure). Efflux gastensions and HbO₂ content can be monitored (RapidLab 840 blood gasanalyzer and co-oximeter, Siemens A G, GDR). O₂-loading rates andefficiency can be determined by perfusing deoxygenated suspensionsthrough the lung while ventilating with 21% O₂, 5% CO₂, bal. N₂;O₂-unloading rates and efficiency can be determined by perfusingoxygenated suspensions through the lung while ventilating with O% O₂,10% CO₂, bal. N₂. Loading/unloading rates for nanoparticles with low,normal, and high p50 (as described above) can be determined andevaluated for responsiveness to pH, temperature and pCO₂ in comparisonto values obtained for human RBCs.

Example 5 Sustenance of Nanoparticle O₂ Delivery by Reducing the Rate ofMetHb Formation

Met-Hemoglobin (MetHb) accumulation during cyclic O₂ loading/unloadingmay be quantified using a thin film rotating tonometer in the presenceof physiologic buffer (e.g. Krebs) or human plasma. A goal of metHbaccrual may be to limit accrual to 10% following three hours ofsimulated circulation, with pO₂ cycling between 120 to 50 Torr.Nanoparticles of the disclosure comprise a reductant, and varying themolar ratio of reductant to hemoglobin (for example, between about 0.5to about 10×molar ratios) is one means to affect metHb accrual. Samplescan be obtained at time 0, 10 min, 30 min, 1 hour, 3 hours and therelative % age of oxy-, deoxy-, and metHb will be determined (RapidLab840 blood gas analyzer and co-oximeter, Siemens AG, GDR).

Example 6 Maintenance of Sterility of Nanoparticle Formulations DuringProduction and Prolonged Storage in Lyophilized Form

Sterile production, prolonged stability of nanoparticles in alyophilized form, and reconstituted recovery of O₂ binding/releaseproperties may be demonstrated. In addition, nanoparticle asepticfiltration may be optimized. Recovery of nanoparticle functionalities(<10% change from baseline) following lyophilization and storage (up to12 months) at 4°, 25°, and 40° C. can be confirmed.

Example 7 Evaluate and Limit Nanoparticle NO Sequestration andVasoactivity

Oxygen carrying nanoparticles of the disclosure may be optimized forminimum NO binding throughout cyclic O₂ loading/unloading. The rate andtotal NO consumption for nanoparticles formulations may be determined,employing a validated nitric oxide (NO) consumption assay. Hemoglobinpayload and membrane features may be varied to limit NO sequestration towithin 10% that of normal RBCs. Nanoparticles may be optimized forminimum vasoactivity throughout O₂ loading/unloading cycles. Theseexperiments may correlate NO sequestration rates to vasoactivity in astandard vascular ring array (VRA), both as a function of O₂ content.Change in vessel tone may be benchmarked (within 10%) to values fornormal RBCs to confirm that any NO trapping is below physiologicallysignificant levels.

To further evaluate this feature, nanoparticle formulations wereproduced with varied hemoglobin packing and shell crosslinking (Table 2)and NO scavenging was quantified and compared to that for intact RBCsand free Hb. The results of these experiments (FIG. 4-7) demonstrate: 1)total NO sequestration by nanoparticle formulations is less than thatfor RBCs and free Hb and varies more so as a function of shell characterand Hb packing density (FIGS. 6); and 2) the rate of NO sequestration bynanoparticle formulations varies principally as a function of shellcrosslinking and can be reduced below the rate for intact RBCs (FIGS. 5and 7).

TABLE 2 Nanoparticle formulations tested Formulation Hb density [Hb](μM) Crosslinking F1 Low 93 Medium F2 High 372 Medium F3 Medium 170 LowF4 Medium 170 High

Example 8 Determine O₂-Delivery Efficacy of Nanoparticles

Demonstrating HIF-1α stabilization is the gold-standard measure ofinadequate O₂ delivery to tissue. To accomplish this, a novel dynamicwhole animal HIF-reporting model can be used to characterize the abilityof oxygen-carrying nanoparticles of the disclosure to maintain tissue O₂delivery during a stepwise reduction in native Hb. Normovolemichemodilution is one means by which to simulate acute traumatic bloodloss and fluid resuscitation in the field; this approach will controlfor hypotension, eliminating hypoperfusion it as a confounder fordiminished blood O₂ content. Primary outcomes of interest are: 1)survival; 2) tissue PO₂ and 3) HIF (ODD)-luciferase signal. Means tomonitor HIF expression/stabilization non-invasively during acute anemiaand its resolution, by quantitating whole-animal bioluminescence inHIF-α(ODD)-luciferase mice have been described and validated. See, forexample, Safran M, Kim W Y, O'Connell F, Flippin L, Gunzler V, Horner JW, Depinho R A, Kaelin W G, Jr. Mouse model for noninvasive imaging ofhif prolyl hydroxylase activity: Assessment of an oral agent thatstimulates erythropoietin production. Proc Natl Acad Sci USA. 2006;103:105-110; or Tsui A K, Marsden P A, Mazer C D, Adamson S L, HenkelmanR M, Ho J J, Wilson D F, Heximer S P, Connelly K A, Bolz S S, LidingtonD, El-Beheiry M H, Dattani N D, Chen K M, Hare G M. Priming ofhypoxia-inducible factor by neuronal nitric oxide synthase is essentialfor adaptive responses to severe anemia. Proc Natl Acad Sci USA. 2011;108:17544-17549; each hereby incorporated by reference in its entirety.

As such, a stepwise increase in real-time whole body bioluminescence isobserved as Hb falls; paired assessment of HIF protein levels (Western)and HIF-dependent RNA expression in multiple tissues confirm thenon-invasive in vivo assessment of HIF signaling (FIG. 8). In thismodel, the increase in HIF-luciferase expression occurs as early as 6hours after induction of anemia with a peak expression at˜24 hours, andis proportional to the acute decrease in Hb level and pO₂. As [Hb]recovers by physiological mechanism (endogenous erythropoietin) over 7days, HIF levels return to baseline (FIG. 8E). Hypoxia exposure servesas a positive control for HIF expression in this model.

Using the HIF-1α(ODD) luciferase mouse model, the ability ofoxygen-carrying nanoparticles to restore tissue O₂ delivery followingreduction in native [Hb] may be characterized. An exchange transfusionmay be performed with nanoparticles (normalized total hemoglobin) orpentastarch (normovolemic anemia, control) to study O₂delivery+/−hypoxic stress by in vivo bioluminescent imaging and tissueoxyphor quenching. In a separate hemodilution group, hemoglobin may benormalized by re-infusing shed murine RBCs to establish referenceHIF-luciferase and oxyphor activity; Nanoparticles quenching may bewithin 10% that achieved by re-infusing murine RBCs. Pharmacokinetics(PK) of the nanoparticles particle may also be determined. Nanoparticlesmay be labeled with ^(99m)Tc and administered as described above.Activity may be measured serially, and PK parameters may be calculated.75% retention may be expected at 3 hours, with duration of circulationmatched to duration of efficacy using HIF-luciferase and oxyphorquenching.

Example 9 Evaluation of Nanoparticle Efficacy in a Rodent HemorrhagicShock Model

Polyethyleneimine polymers were grafted with hydrophobic alkyl groups bycovalent means. Palmitic acid was activated with the carbodiimide EDAC(1-ethyl-3-(3-dimethylaminopropyl) carbodiimide, hydrochloride) followedby addition of the polymer to achieve greater than 50% functionalizationof free primary amine groups and a partial functionalization of thesecondary amines. The amphiphilic polymer was dispersed in anhydrouschloroform and gently vortexed for 2-5 minutes. The measurement ofhydrodynamic diameter of this construct confirms the formation of a 7-10nm sized unimolecular inverted micellar (IM) structure,

Concentrated and purified hemoglobin and 2,3-DPG mixture, and methyleneblue were suspended in aqueous medium and was added to the organicsolvent mixture of the IM. This bi-phasic mixture was allowed to settledown and inverted several times until the all the payloads weretransferred to the organic layer comprising of IMs. The transfer can beachieved by briefly shaking/swirling and inversion or a combinationmethod. Hemoglobin was human hemoglobin extracted and purified fromexpired RBCs. Hemoglobin was stabilized as carboxyhemoglobin (HbCO),purified via ion-exchange chromatography, and concentrated usingultrafiltration to 4.0 g/dL, The concentration of hemoglobin used togenerate the nanoparticles was 10 mg/mL. The concentration of 2,3-DPGwas 10 mg/mL. The concentration of leucomethylene blue was 5 mg/mL. Thepayload-incorporated IM was transferred to a long neck glass tube and tothis equal volume of nanopure water (0.2 uM) was added. The mixture wasbriefly sonicated for 1-2 min followed by a slow evaporation of theorganic solvent under reduced pressure following a reverse phase solventevaporation protocol. The removal of organic solvent was confirmed bythe prolonged rotary evaporation and dialysis. In a typical preparation,nanoparticles comprised an average of 4000 hemoglobin molecules pernanoparticle. Following the self-assembly and reverse phase solventevaporation, the nanoparticles were subjected to surface chemicalcross-linking using Sulfo-EGS (ethylene glycolbis[sulfosuccinimidylsuccinate], PBS, pH 8.5) in combination withhydroxylamine for 5 h at 37° C. The intramolecular crosslinking step isdevoid of use of any chemical crosslinker. Nanoparticle sizes, shape,and morphology were measured by TEM, DLS, and AFM among other methods.Nanoparticles had a hydrodynamic diameter of 150-180 nm, or 173±10 nmafter re-suspension, with polydispersity of 0.26±0.01, and zetapotential of ˜12±2 mV. Crosslinking has limited effect on particle sizeand zeta potential: 167±56 nm, +7±2 mV, respectively. Assays wereperformed as described in Pan D, Caruthers S D, Hu G, Senpan A, Scott MJ, Gaffney P J, Wickline S A, Lanza G M. Ligand-directed nanobialys astheranostic agent for drug delivery and manganese-based magneticresonance imaging of vascular targets. J Am Chem Soc, 2008;130:9186-9187.

Example 10 Evaluation of Nanoparticle Efficacy in a Rodent HemorrhagicShock Model

Nanoparticle efficacy was evaluated in a rodent hemorrhagic shock model.Nanoparticles were produced as described in Example 9. Rats (SpragueDawley, 400 g, N=3) were anesthetized (isoflurane) and underwenttracheotomy with institution of mechanical ventilation (RA) andcannulation of the jugular and femoral veins and the carotid and femoralarteries. After establishing baseline values for blood O₂ content and AVO₂ difference, 25% blood volume was removed, new values were obtained,and animals were resuscitated with an equal volume of the bloodsubstitute (N=2) or normal saline (N=1). Nanoparticles (NP) weresuspended at 40 wt/vol %, with suspension [Hb] of 4 mM. FIG. 9 shows theoutcome of the experiment. The plot illustrates an expected, strikingincrease in the AV O2 difference with blood removal (rising from 24 to67%), that (A) persisted following resuscitation with normal saline and(B) resolved following resuscitation with the blood substitute(normalizing from 67 to 31%). In (C), a difference was not observed inthe hemodynamic effect afforded by either resuscitation fluid,suggesting that the benefit in O₂ delivery from the blood substitutearises from improved O₂ content, in addition to restoration of bloodpressure. Moreover, unlike other hemoglobin-based blood substitutes,which are known to cause vasoconstriction and hypertension from NOsequestration; the NP-based blood substitute reconstituted normalhemodynamics. This further supports the in vitro data that the NP doesnot induce significant NO sequestration.

Example 11 Preparation of Nanoparticles

A mixture of hemoglobin (Hb) and amphiphilic polymer mixture(preloaded/not with 2,3-DPG and LMB) underwent self-assembly inphosphate buffer (PB) at pH 7.3 using a microfluidization/homogenizationtechnique. The mixture was vigorously vortexed to homogeneity followedby continuously processing thereafter at 18000 psi for 4 min with an LV1Microfluidics emulsifier. [Hb] in the buffer can be titrated todifferent concentrations, for example between 100, 150, 200, 250 and 300mg/mL. Nanoparticle surface chemical cross-linking can utilizeSulfo-EGS, in combination with hydroxylamine (PB buffer, pH 8.5, 5 h,37° C.), followed by dialysis against 50 mM PB to remove the sulfo-EGSby-product. Particle size, polydispersity, and zeta potential for eachnanoparticle formulation can be evaluated as described earlier. The fullpreparation was dialyzed (100 kD membrane) against infinite sink of PBS.The nanoparticles (NP) were collected and tested for free Hb using theDrabkins reagent.

To dialyze against PBS, any suitable dialysis system may be used.Although the procedure is described for the Float-A-Lyzer G2 device,alternative systems are known in the art. To pre-wet the membrane,glycerin was removed to achieve maximum membrane permeability followingthis soaking procedure. Briefly, the cap was unscrewed at the top of thedevice, the device was filled with 10% ethanol (EtOH) solution (inddH₂O), the cap replaced, and then the body of the Float-A-Lyzer G2 wasthreaded through the hole in the flotation ring and the ring was snuglypulled up beneath the collar of the top piece. The device+floatationring was placed in an 80 ml beaker filled with 70 ml of 10% EtOHsolution for 10 minutes with stirring at 300 rpm. The device+floatationring was removed from the beaker, the floatation ring removed and thecap unscrewed to aspirate out the EtOH inside the device. Any remainingdrops of EtOH were removed by inverting the device and shaking. Next,the device was flushed thoroughly with deionized (DI) water, and thenfilled with DI water and re-capped. The capped device was placed in thefloatation ring, and then the device+floatation ring was placed in abeaker with 70 ml DI water for 15 minutes with stirring at 300 rpm. Thewater was removed as described above for the EtOH. The device wasflushed again with DI water and excess water removed by gentle inversionand shaking.

After pre-wetting the Float-A-Lyzer G2, the membrane was conditionedwith the dialysate buffer by rinsing the inside of the membrane severaltimes with PBS. Excess buffer was removed, and the device was loadedwith 900 ul of the nanoparticle preparation. The device was placed inthe floatation ring and then dialyzed in 70 ml of PBS for 20 minutes atroom temperature with stirring at 300 rpm. The device was removed fromthe dialysate after 20 minutes.

Following dialysis, the 25 ml volume of dialysate was concentrated usingan Amicon Ultra 15 Centrifugal filter, which was washed in ddH₂O priorto use. Briefly, the Amicon Ultra filter was washed by adding 15 ml ofddH₂O to the top cassette. The filter was centrifuged at 3400×g for 60minutes and 4° C. Once spun, the cap was removed and the flow through atthe bottom of the conical and any liquid remaining in the top cassettewas discarded. 15 ml of the dialysate was added to the cassette andcentrifuged at 3400×g for 30 minutes and 4° C. After 30 minutes another10 ml of dialysate was added to the filter, and the filter was againcentrifuged at 3400×g for an addition 60 minutes at 4° C. Once it hasfinished spinning, the solution was removed from the filter cassetteusing a 200 ul pipette. This solution will contain the concentrated Hb.If the amount of solution is greater than 1.3 ml, spin for a longerperiod of time. Once the 25 ml volume of dialysate has been concentratedto less than 1.3 ml, remove the solution from the cassette with a 200 ulpipette and dilute it to a 1.3 ml total volume using PBS.

To test for free Hb, a Drabkin's assay was run on the sample using a 1:1dilution with Drabkin's reagent following Manufacturers protocol. 300 ulof solution was added to each well (in triplicate) and the absorbance ofcyanomethemoglobin was recorded at a fixed wavelength (540 nm).Thehemoglobin concentration of the original hemoglobin solution wasmeasured using the following equation: Heme (mM)=(sample absorbance @540nm×dilution factor) (Extinction coefficient @540 nm×path lengthcorrection); Dilution; factor=2; Extinction coefficient=11 mM⁻¹cm⁻¹;Path length correction=0.8 for 300 μl in the 96 well plate; For Hbtetramer, the answer was divided by 4.

What is claimed is:
 1. A method for providing oxygen to an organ exvivo, the method comprising perfusing an organ with an effective amountof an oxygen-carrying nanoparticle, wherein the nanoparticle has asubstantially bi-concaved disc shape and comprises an aqueous core, abi-layered shell comprising an amphiphilic polymer, and a payload; andwherein the bi-layered shell has a hydrophilic outer layer, ahydrophilic inner layer, and a hydrophobic region between thehydrophilic outer layer and the hydrophilic inner layer; the amphiphilicpolymer comprises a branched, amine-containing polymer linked to alipid; and the payload comprises an oxygen-carrying agent, an allostericeffector, and a reducing agent.
 2. The method of claim 1, wherein theamphiphilic polymer comprising the hydrophilic outer layer of the shellis derivatized with polyethylene glycol, such that the particle has azeta potential of about −15 mV to about +15 mV.
 3. The method of claim1, wherein the average diameter of the nanoparticle is from about 150 nmto about 300 nm, and the average height of the nanoparticle is fromabout 30 nm to about 80 nm.
 4. The method of claim 1, wherein theoxygen-carrying agent is synthetic hemoglobin or naturally occurringhemoglobin.
 5. The method of claim 11, wherein the allosteric effectoris selected from the group consisting of 2,3-diphosphoglycerate(2,3-DPG), inositol hexaphosphate (IHP), pyridoxal-phosphate (PLP), and2-[4-[[(3,5-dimethylanilino carbonyl]methyl]-phenoxy]-2-methylpropionicacid.
 6. The method of claim 1, wherein the reducing agent is selectedfrom the group consisting of leucomethylene blue, glutathione andascorbate.
 7. The method of claim 1, wherein the nanoparticle comprisesabout 3000 to about 10,000 hemoglobin molecules.
 8. The method of claim1, wherein the nanoparticle comprises about 20% to about 60% (w/v)hemoglobin or about 30% to about 60% (w/v) hemoglobin.
 9. The method ofclaim 1, wherein the nanoparticle limits the oxidation of hemoglobin toabout 10% or less of the total concentration of hemoglobin in thenanoparticle.
 10. The method of claim 1, wherein the branched,amine-containing polymer is selected from the group consisting of apolyethyleneimine branched polymer, a PAMAM dendrimer, a star polymer,and a graft polymer.